Linux/Proton fix: Steam says “Running” but no game window appears

[Ruzo]

Black Flag Resynced had been launching normally for me, then it suddenly stopped working later the same day. Steam changed the Play button to Stop and acted as though the game was running, but there was no splash screen, Ubisoft Connect window, or game window.

My setup

• Omarchy/Arch Linux
  
• Hyprland 0.55.2 on Wayland
  
• RTX 5090 with NVIDIA 610.43.02
  
• Native Steam 1.0.0.85-7
  
• Proton Experimental

What was actually happening

I initially suspected Wayland, Hyprland, NVIDIA, or an off-screen window. However, the game wasn’t getting far enough to create a window.

The running processes included Ubisoft Connect components such as

UbisoftGameLauncher.exe

,

upc.exe

, and

UplayWebCore.exe

, but

ACBlackFlag.exe

itself never started.

Ubisoft Connect was hanging while loading its embedded Chromium/CEF browser profile. Its cached database files kept entering recovery during every launch attempt. This left Steam permanently showing the game as running while only the launcher remained alive in the background.

The fix

1. Stop the game in Steam.
   
2. Exit Steam completely so none of the Ubisoft launcher processes are using the cache.
   
3. Rename the following folder:

<SteamLibrary>/steamapps/compatdata/3751950/pfx/drive_c/users/steamuser/AppData/Local/Ubisoft Game Launcher/cache/http2

For a standard native Steam installation, this command creates a timestamped backup:

cache="$HOME/.local/share/Steam/steamapps/compatdata/3751950/pfx/drive_c/users/steamuser/AppData/Local/Ubisoft Game Launcher/cache"
mv "$cache/http2" "$cache/http2.backup-$(date +%Y%m%d-%H%M%S)"

If the game is installed in another Steam library, use that library’s

steamapps

directory instead.

After launching Steam and starting the game again, Ubisoft Connect automatically created a clean

http2

folder. This time

ACBlackFlag.exe

started and the game window appeared normally. Ubisoft Connect may ask you to sign in again.

Important notes

• Do not delete the entire Proton prefix or

  compatdata/3751950

  directory.
  
• This cache reset does not remove the game or its save files.
  
• Renaming the folder instead of deleting it makes the change reversible.
  
• Once the game is working, the backup can be deleted.
  
• Do not upload or share the backup because it may contain Ubisoft browser or session data.

This fix is specifically worth trying when Steam says the game is running, Ubisoft Connect stays alive in the background, but the actual game executable and window never appear.

[Nupidstoob]

Thanks, this is what was happening to me, I thought it had to do with nvidia caching but I couldn't really nail the root cause.

[snuggieman]

this worked for me the first time but its inconsistent. the second time it didnt work but once I changed proton versions it then worked. doesnt matter which version, just switching back and forth seems to sometimes fix it

[Ferrito]

good job. Well done.