I really hate to resurrect an old thread, but this is the EXACT same problem that I am still having. There are 24 (yes, TWENTY-FOUR!) achievements that pop every time that I load Old World. (My husband has the same issue but with a different number of achievements)

Play a LAN Game
Play a Network Game
Play a Single Player Game
Play a Free-for-all Game (>2 Players)
New Difficulty
The Mythical Beast
What's the Worst that Happens?
Hatti
Hittite Iron
Hittite Paganism
Christianity
Jackpot
Cothon
Al Khazneh
Royal Library
Necropolis
Jerwan Aquaduct
Via Recta Souk
The Clergy
Riders
Fountainhead
Military Prestige
Good


While they all show on the Overview page in GOG Galaxy as being earned, if I go to the details page of achievements, there is no little trophy with a date and it doesn't appear to actually be listed as being earned. See attached images - the What's the Worst That Happens achievement shows as being earned, but in the full list it is not.

Also, oddly - if I open the game, 24 achievements pop. If I close it then open again, only 18 pop. Repeating this gets 12 and then 6... and then the next time I open it goes back to 24.

And one more odd thing: SOMETIMES the first achievement to pop doesn't show a name, it just shows "galaxy_notifications__achievement_unlocke..." though that may be completely unrelated.