Background: game created in 20w51a IIRC - I'm not 100% sure - I've done two "create backup" steps since starting the game.

If I ride my mine cart it stops suddenly in a particular spot.  The moving mine cart sound continues, but I can't stop or exit the mine cart.  I can interact fully with things around me - I can mine nearby blocks, open inventory, etc.  Also, time continues to pass (gets darker).

If I "save and exit to main menu" the game hangs while "saving game."  At that point the only resort is to use task manager to kill the java process.

Restarting and reloading the game, the bug repeats - ride the mine cart, get stuck.

Log file attached just in case it helps.