I FOUND THE SOLUTION! Searching around, I've found a suggestion from the developer in a Steam forum:
Have you tried running the game as administrator?
This did the trick for me:
1. Using Explorer, go to the Phantom Doctrine directory
2. You should see the file IWTB.exe
3. Launch it as an administrator (i.e. right-click to open the context menu, then choose "Run as Administrator")
4.a If the game freezes again, kill it again (*), then go to 6
4.b. Else, let the game launch until you reach the game menu (Start, Load, etc.)
5.b. Exit the game, using the "Quit" option
6. Now, you can restart the game normally (i.e. through Galaxy, without needing administrator privileges).
(*) in one attempt, it succeeded only after I killed "IWTB-Win64-Shipping.exe", the child process of "IWTB.exe". I believe this child process being killed, "IWTB.exe" then exits normally, which could have a different outcome from killing "IWTB.exe" directly. I suspect this game installs something when started the first time since update, or whatever, and for that, it needs admin privileges.
\o/
This bug reappeared today, and I tried again launching from the game folder, as admin or not, trying ti verify and repair, and I had no success. I had prepared an email for support@creativeforge.pl when (I kid you not) I tried again, this time, from GOG... And for some reason, it works now.
o.O
P.S.: You'll find below all my previous (failed) attempts to fix this.
BroncoP: Weird, after playing for several days, the game now gets stuck at the initial splash screen. Verifying, removing and re-installing didn't help. Any hints?
Similar problem: Using GOG Galaxy 2, first launch, frozen on the splash screen.
:-(
Editbozfoogle: In my case Galaxy hadn't fully downloaded the game. I made it verify files and it downloaded an additional 52mb. After that the game started without issue.
Tried that and while it downloaded 53Mb of files for some reason, I'm still stuck at the splash screen.
:-(
Edit Looking at the process with Process Explorer, I get the impression the game is waiting. I cannot be sure, but the stacks seem stuck at WinAPIs like WaitForMultipleObjects. There's also an insane amount of threads trying to "PrintScriptCallstack" (who are also waiting "WaitForSingleObject). I don't know if the stacks are correct, and I don't even know if this is relevant, but "waiting" is clearly what I feel this game is doing, when I launch it.
Also tried without GOG overlay, no success. My NVidia drivers are up-to-date. Tried again to verify/update the game files, and for some reason, it downloaded the 53Mb again, flashed a window (I suspect this is the Unreal Engine or something), and ended "successfully".
The game is still frozen at launch.
Edit Uninstalled it, then reinstalled it. Same problem: The game freezes at launch, on the splash screen.