Is this just the first time on Sanctuary? I have only played that part in multiplayer with a friend on Windows. It may be the same MP4 issue. I have a memory of something not playing there.
I still have not been able to solve the MP4 issue at all, I have tried a number of different fixes to no avail.
And @GlennSteenn, thanks for the info. I will try that on a character I got to that point to test the issue. See if that works. I triggered it once, but have not been able to again with a different character.
You can see some output from WINE if you run Lutris from the command line. Apparently you can get more verbose output from UE4 by adding some options to the Engine.ini file. But editing
/users/username/My Documents/My Games/Borderlands 3/Saved/Config/WindowsNoEditor/Engine.ini within the wine prefix didn’t help as it seems to be rewritten as soon as the game is started. Though I have zero Unreal Engine (4 or otherwise) experience in terms of debugging, so it may be otherwise possible to get debug output.
Edit: I have written an installer that performs the mf-install steps for you, it is submitted and waiting for approval. The initial one I published does work or fix the problem, so if you go to the Borderlands 3 page (need to show unpublished games via search) and try to the installer it will NOT work. It is an old version I was testing. I will update this post once the current version I have is published.