Cuphead (268910) freezing now that didn't before no known changes

Version: Proton 4.11-13
Game: Cuphead

I've bought and downloaded Cuphead for play on Steam on Ubuntu 19.10 (5.3.0-46-generic). Everything was going well through last autumn and winter and then I left it for several months and have just come back to the game not loading.

Obviously some change must have occurred, but I don't know where to begin troubleshooting this issue.

The game brings up the first box in Steam that says the game is loading, and then the full screen of the game itself comes up and I can hear the initial sound effects (if you know the game it is like putting a needle on a record before the song begins), but the game freezes at this point (sound continues it just doesn't move on to the credits and the start menu). I have attempted to verify the game files, and I have also attempted to uninstall and reinstall the game, neither had any effect on the outcome.

Any advice on what can be done to troubleshoot this issue and get it to work would be very welcome.

No source file, test, or entry point is named. Start by reproducing the freeze with Proton 4.11-13 on Ubuntu 19.10 and collecting the Proton or Steam launch output plus relevant system details; done means identifying a reproducible cause or documented compatibility fix.