All right, that means at least the main game is not broken but something in the actual contents of the "Deluxe Upgrade". Which still sucks but not as much. And it is still odd that, again, this is not an issue for everyone but some people. So yet not broken but conflicting files.

I'm pretty sure its the "steam_api64.dll" error, as the crash log says. Because i dont have any errors in the Steam version of the game. And the GOG version of the dll does not have a digital signature. Not sure if it matters

I tried the thing about deluxe edition upgrade
Well, at first i thought just deleting the deluxe upgrade content and just leaving E2, and E3 (the 2 other main episodes) in the DLC folder would work for a quick test but no, in that situation it would crash the same way
So i had an idea and renamed completely the DLC folder: the game worked/launched, but only with episode 1

As i thought it would be quite hard to swallow, i uninstalled all and reinstalled only the game itself with all 4 episodes but no deluxe upgrade bonus: The game launched (which is a progress compared to previously), cannot test if episodes 2, and 3 can be played (it requires episode 1 to be played and finished, which is too long for a quick test, though i may try to use my steam save) but at least this time it wouldnt crash just because they are here

Needless to say someone (gog, square, deck nine ?) screwed up with the whole DLC check/verification/validation because too much used to paranoid DRM (Before the Storm uses denuvo on top of steam) and are NEW to the whole concept of DRM free and 'TRUST in your customers"

Well, so Before the Storm's case seems "solved", except the deluxe content is so far paid for nothing

Sadly, afaic, Before the Storm, the merc-outsourced fan service prequel, is really not my favorite at all, i was quite mixed bag/disappointed by it, and my main concern is that i'd like the REAL first game, the one by DontNod, to work

You can, just copy all files in ...\AppData\LocalLow\Square Enix\Life Is Strange_ Before The Storm\Saves from 76561197995054635 (steam) to 76561201163648751 (gog).

Hi all! Just an update, a few days ago I posted here and contacted GOG support. Today I got a reply saying I should edit common.dll and change all three "C5 FD EF" to "66 0F EF", save it, and try to launch the game. And it helped me. So maybe some you can try this and see if it helps. Hope the rest of you fix your problem soon!

Looks like GOG does read this forum after all - a forum member discovered this fix and and posted yesterday - https://www.gog.com/forum/life_is_strange_series/wont_launch_possible_fix/post1

Glad you've now got it working though :)

Haha, yeah, I bet they do. Good luck to you all fixing your issues!

Reading the forum there seem to be multiple problems. A fault in the common.dll and a fault with the DLC.

I have the problem with the common.dll in Windows 10. I discovered that reading the Windows log (open the Event Viewer and go to Windows Logs / Application). One of the errors in the log mentioned the common.dll and the LifeIsStrange.exe.
Now I never used a Hex-editor before, but luckily there is Hex Editor Pro in the Microsoft Store. This is the safest way to get an Hex Editor I think, I don't feel safe to download just another executable from the internet.
Using the Hex Editor Pro was easy, just enter the C5 FD EF in the search box. Then in the main window alter the C5 and FD with 66 and 0F (three times in total). This did work for me.

I hope this description helps ohter people who are not customed to using hex editors - like me.

Awesome, thanks for the report, am going to try it!
Edit: Can't find the common.dll in the game files, the 2 included in the GalaxyClient folder don't contain 'C5 FD EF'.
Disabling the Deluxe content pack allows me to run the game.

The common.dll HexFix is a workaround for Life is Strange, not Before the Storm. The file is located in
...\Life is Strange\Binaries\Win32

The issue with BtS is linked to steam_api64.dll and does (for some) only affect the Deluxe Upgrade.

Ah, thanks, that explains, hadn't caught that part.:)
Yeah, uninstalling or disabling the Deluxe stuff lets me at least start the game.
Guess I'll have stuff to come back to once I'm done when the devs fix that issue.;)

I do agree that having this kind of DRM bumbling on a DRM free platform is kind of dumb.

W7Pro 32bit. Editing common.dll doesn't help me. The steam version on the same PC works OK. When I run the GOG version, a new Unreal dmp file appears in the Documents\My Games\Life is Strange\LifeIsStrangeGame\Logs folder each time it starts. Using Windbg, I learned the following from it (The steam version does not create these dmb files. I have no idea if it will help anything):

Microsoft (R) Windows Debugger Version 6.11.0001.404 X86
Copyright (c) Microsoft Corporation. All rights reserved.


Loading Dump File [C:\Users\user\Documents\My Games\Life is Strange\LifeIsStrangeGame\Logs\unreal-v8623-2020.06.14-23.41.17.dmp]
User Mini Dump File: Only registers, stack and portions of memory are available

Symbol search path is: *** Invalid ***
****************************************************************************
* Symbol loading may be unreliable without a symbol search path. *
* Use .symfix to have the debugger choose a symbol path. *
* After setting your symbol path, use .reload to refresh symbol locations. *
****************************************************************************
Executable search path is:
Windows 7 Version 7601 (Service Pack 1) MP (4 procs) Free x86 compatible
Product: WinNt, suite: SingleUserTS
Machine Name:
Debug session time: Sun Jun 14 23:41:17.000 2020 (GMT+2)
System Uptime: 0 days 11:14:11.131
Process Uptime: not available
................................................................
......
This dump file has an exception of interest stored in it.
The stored exception information can be accessed via .ecxr.
(1610.25e8): Illegal instruction - code c000001d (first/second chance not available)
eax=00000087 ebx=063a2480 ecx=063a07e8 edx=0060e938 esi=063a2440 edi=0060ec70
eip=779b6b94 esp=0060e930 ebp=0060e940 iopl=0 nv up ei pl zr na pe nc
cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00000246
*** ERROR: Symbol file could not be found. Defaulted to export symbols for ntdll.dll -
ntdll!KiFastSystemCallRet:
779b6b94 c3 ret

Try the TLDR of the top answer here: https://stackoverflow.com/questions/30019889/how-to-set-up-symbols-in-windbg

Thanks for the advice, but it's probably over my superpowers;). Anyway, my GOG version has an Unreal problem (Steam version is OK). Why, I have no idea, I thought that the GOG and Steam versions differ only in LifeIsStrenge.exe and Galaxy.dll, common.dll and steam_api.dll. If somebody interested in the dmb file, I will send it, otherwise I will probably wait patiently ... Or I will try a refund to motivate GOG to solve it.

Solved BTS DLC crashing, if anyone is feeling adventurous and wants to edit steam_api64.dll in a hexeditor, you only need to make a single change:

search for "48 83 EC 38 FF"
and replace it with "31 C0 FF C0 C3"

of course, you still need the DLC installed. Let me know if this works for you guys.

EDIT: info of my install - Life is Strange: Before the Storm (with DLC installed) gog version 1.0_(38099)
SHA1 hash of my original steam_api64.dll file (so you can verify you have the correct version): 3e091f273ffeb29cf435b2c398d3cffc4d6b1d2d