It seems that GOG has made some changes to its API today --- intentionally or not is anybody's guess. It appears that GOG now hides download file information about some DLCs that are not directly available for sale on the website (primarily kickstarter and pre-oder DLCs). As far as I can deduce no files have been actually removed, but the information on them has been hidden from the general public. Since I don't own the vast majority of these, the upshot of the change is that MaGog can no longer monitor changes in these files. This does not affect gogdb because I believe gogdb never listed or tracked these DLCs in the first place.

Here is the list of now hidden DLCs (N =117):
25th Ward: The Silver Case, The ===> DLC: Digital Art Book
25th Ward: The Silver Case, The ===> DLC: Digital Soundtrack
Absolver ===> DLC: Pre-Order
Ashes of the Singularity [removed on Feb 21, 2017] ===> DLC: Gauntlet
Banner Saga 3 ===> DLC: KS Banner Bearer
Banner Saga 3 ===> DLC: KS Bannerfolk
Banner Saga 3 ===> DLC: KS Dredge Loot
Banner Saga 3 ===> DLC: KS Human Loot
Banner Saga 3 ===> DLC: KS Sweetener
Banner Saga 3 ===> DLC: KS Troll Ward
Banner Saga 3 ===> DLC: KS Varl Loot
Banner Saga 3 ===> DLC: Kivi
Banner Saga 3 ===> DLC: Petrie Clan Ring
Banner Saga 3 ===> DLC: Sculptor's Tools
Banner Saga 3 ===> DLC: Shadow Walker
Banner Saga 3 ===> DLC: Shield Cleaver
Banner Saga 3 ===> DLC: Soundtrack Bonus
Broken Sword 4: The Angel of Death (Secrets of the Ark) ===> DLC: OST
Broken Sword: Director's Cut ===> DLC: OST
Cossacks 3 ===> DLC: Early Bird
Cossacks 3 ===> DLC: Soundtrack
Cultist Simulator ===> DLC: Perpetual Edition Content
Death's Gambit ===> DLC: Chosen of Death Pack
Dungeons 3 ===> DLC: Horde Throne Room
Dungeons 3 ===> DLC: Soundtrack
Dungeons 3 ===> DLC: Undead Throne Room
Dying Light: The Following - Enhanced Edition ===> DLC: Crash Test Skin Pack
Dying Light: The Following - Enhanced Edition ===> DLC: Harran Military Rifle
Fear Effect: Sedna ===> DLC: Collector's Edition Bonus
For The King ===> DLC: Kickstarter Backer Plus
For The King ===> DLC: Kickstarter Backer Reward
Frostpunk ===> DLC: Digital Artbook
Frostpunk ===> DLC: Season Pass
Hat in Time, A ===> DLC: Nyakuza Metro Pre-Order
Headlander ===> DLC: Soundtrack
Hellblade: Senua's Sacrifice ===> DLC: Comic
Hellmut: The Badass from Hell ===> DLC: Deluxe Edition Goodies
Hello Neighbor ===> DLC: Alpha Builds
Hyperdimension Neptunia Re;Birth1 ===> DLC: Deluxe Pack
Hyperdimension Neptunia Re;Birth2: Sisters Generation ===> DLC: Deluxe Pack
Hyperdimension Neptunia Re;Birth3 V Generation ===> DLC: Deluxe Pack
Incredible Adventures of Van Helsing: Final Cut, The ===> DLC: Textures
Legend of Heroes: Trails of Cold Steel II, The ===> DLC: Trails in the Sky Costumes
Little Nightmares ===> DLC: Fox Mask
Little Nightmares ===> DLC: Scarecrow Sack
Little Nightmares ===> DLC: Tengu Mask
Little Nightmares ===> DLC: Wallpaper
Master of Orion ===> DLC: Elerian Fiefdoms
Master of Orion ===> DLC: Gnolam League
Master of Orion ===> DLC: Terran Khanate
Master of Orion ===> DLC: Trilarian Shoal
My Memory of Us ===> DLC: Collector's Edition Bonus
Obduction® ===> DLC: Kickstarter Tier 1
Obduction® ===> DLC: Kickstarter Tier 2
Pathfinder: Kingmaker - Explorer Edition ===> DLC: Artbook & OST
Pathfinder: Kingmaker - Explorer Edition ===> DLC: Chris Avellone Adventure Module
Pathfinder: Kingmaker - Explorer Edition ===> DLC: In-Game Pet - Red Panda
Pathfinder: Kingmaker - Explorer Edition ===> DLC: In-game player's portraits
Pathfinder: Kingmaker - Explorer Edition ===> DLC: Kickstarter Tier 1
Pathfinder: Kingmaker - Explorer Edition ===> DLC: Kickstarter Tier 2
Pathfinder: Kingmaker - Explorer Edition ===> DLC: Kickstarter Tier 3
Pathfinder: Kingmaker - Explorer Edition ===> DLC: Map of Stolen Lands
Pathfinder: Kingmaker - Explorer Edition ===> DLC: Pre-order Bonus
Pathfinder: Kingmaker - Explorer Edition ===> DLC: Premium Digital Copy
Pathfinder: Kingmaker - Explorer Edition ===> DLC: Season Pass
Pillars of Eternity II: Deadfire ===> DLC: Captain's Footlocker
Pillars of Eternity II: Deadfire ===> DLC: Explorer's Pack - Pet Cosmo
Pillars of Eternity II: Deadfire ===> DLC: Explorer's Pack - Tricorn Hat
Pillars of Eternity II: Deadfire ===> DLC: Explorer's Pack Bonus
Pillars of Eternity II: Deadfire ===> DLC: Fig - Cloak of the Obsidian Order
Pillars of Eternity II: Deadfire ===> DLC: Fig - Mātakau
Pillars of Eternity II: Deadfire ===> DLC: Fig - Pet Wurm
Pillars of Eternity II: Deadfire ===> DLC: Korean Localization
Pillars of Eternity II: Deadfire ===> DLC: Pillars of Eternity Owner's Bonus
Pillars of Eternity II: Deadfire ===> DLC: Scavenger Hunt Rewards
Prison Architect ===> DLC: Psychward
Q.U.B.E. 2 ===> DLC: Classic Q.U.B.E. Glove Skin
Q.U.B.E. 2 ===> DLC: Puzzle Pack 1
Q.U.B.E. 2 ===> DLC: Puzzle Pack 2
Railway Empire ===> DLC: OST
Railway Empire ===> DLC: Preorder Super Hudson Skin
River City Ransom: Underground ===> DLC: Kunio & Riki [Kickstarter Exclusive]
River City Ransom: Underground ===> DLC: OST [Kickstarter Exclusive]
River City Ransom: Underground ===> DLC: Weapons [Kickstarter Exclusive]
Seven: Enhanced Edition ===> DLC: Digital Collector's Edition Goodies
Seven: Enhanced Edition ===> DLC: Pre-Order
Sexy Brutale, The ===> DLC: Preorder
Shadows: Awakening ===> DLC: Bonus
Silver Case, The ===> DLC: The Extra Contents
Stellaris ===> DLC: Arachnoid Portrait Pack
Sudden Strike 4 ===> DLC: Battle of Kursk
Sunless Skies ===> DLC: Cyclopean Owl
Sunless Skies ===> DLC: Rabbit Mascot
Surviving Mars ===> DLC: OST
Tahira: Echoes of the Astral Empire ===> DLC: Kickstarter '80s Package
Tahira: Echoes of the Astral Empire ===> DLC: Kickstarter Digital Bundle
Treasure Adventure World ===> DLC: preorder
Urban Empire ===> DLC: Half Timbered Building Pack
Urban Empire ===> DLC: OST
Urban Empire ===> DLC: Two Sides of the Same Coin
Vikings - Wolves of Midgard ===> DLC: Pre-order
War for the Overworld ===> DLC: Arcane Theme
War for the Overworld ===> DLC: Cynical Imp (Charity)
War for the Overworld ===> DLC: Founders Theme (Charity)
War for the Overworld ===> DLC: Founders Theme (Kickstarter)
War for the Overworld ===> DLC: Kickstarter Theme (Charity)
War for the Overworld ===> DLC: Kickstarter Theme (Kickstarter)
We Happy Few ===> DLC: Jolly Brolly
We Happy Few ===> DLC: We All Fall Down
World to the West ===> DLC: Soundtrack
Wuppo [removed on Sep 17, 2019] ===> DLC: Fun Pack
Wuppo [removed on Sep 17, 2019] ===> DLC: Original Soundtrack
Wuppo [removed on Sep 17, 2019] ===> DLC: Shop
XIII ===> DLC: Bonus Items
Yooka-Laylee ===> DLC: Toybox
Ys VIII: Lacrimosa of DANA ===> DLC: Digital Mini Art Book
Ys VIII: Lacrimosa of DANA ===> DLC: Ultimate Resource Bundle

Holy cow, that's a mighty long list.

Were any of them updated/changed till now?

Yes. In most games, when a game installer changes, all its gameplay DLCs (i.e. not bonus DLCs) change too. I don't remember any of these ever changing without the game installer itself having changed, but it may have happened.

P.S. Needless to say, this list only covers pre-legacy games. I'm sure the change has also affected post-legacy games, but I wouldn't know which (and probably will never know, unless GOG reverses this API change).

P.P.S. The list above does not cover all pre-order/kickstarter DLCs out there, so either GOG has been consistently inconsistent, or more are due to disappear.

And today they're all back. I guess that answers the question of intention.

Silly me, of course they change for compatibility.


Heh.

Small update:

* Added "Mac OS X range of versions" to the list of searchable operating systems
--- Note: This is for where GOG now inidicates a minimum and a maximum supported version (e.g. "10.7-10.14"), rather than just a minimum (e.g. "10.7.0+").

Another update:

* Added two new scopes: "Collections" and "Unlisted Items"
--- Note: Collections are store items that bundle together two or more games, which are also available for sale by themselves, into one package.
--- Note: Unlisted Items are store items that have a GOG game page, but are missing from the GOG catalogue.
--- Note: Collections were previously considered to be Premium games, while Unlisted Items were previously searchable via a filter, rather than a scope.

The GOG-MaGog relationship is again undergoing a turbulent period.

As of yesterday, like 14 months ago, MaGog's update run now takes 8-10 hours instead of the normal 2-3 hours. I don't know who's to blame, except that I haven't made any significant changes to MaGog in the last few weeks,

Last time it took upwards of three weeks to resolve, as mysteriously and abruptly as it had appeared.

For now, all I'm doing is moving to a once-a-day MaGog update schedule, instead of the regular four-times-a-day.

Seems to have resolved itself after 48-60 hours. Back to the regular four-times-a-day schedule.

Btw, does it still make sense to update Magog so frequently, now that it's 1 year behind?
Maybe once a day (or more) would be well enough at this point. ¯\_(O_o)_/¯

I don't see the relevance. I want MaGog's information to be as up to date as possible in regards to the games she tracks.

I gather from your comment that you view a MaGog that covers only ~85% of the GOG catalogue pretty useless, but --- judging from MaGog's traffic statistics --- that is not everyone's view. There are still enough things that can be done only through MaGog and --- as I see it --- it's better to have up-to-date information about 85% of the catalogue, than to have it about 0% of the catalogue.

Useless no, just less useful.
Does that old 85% change that much to require 4 updates a day?
Anyway, I was suggesting this just to relieve Gog's servers from unnecessary requests, but if this is still needed then.. nevermind.

Coming back to this, as I just noticed that AF displays the changelog link again on the game page (I don't know since when, but it had stopped after the name change). Don't know if AF and MaGog function similarly on this, but maybe worth taking another look into it?

Perhaps also check the other games you had listed in the "what did just update" a while back?