Tech support issue.
The game appears to be stuck in rollback mode. I was progressing along just fine, a fair distance into the game, when all of sudden is started speeding in reverse, like I was scrolling back -- except I wasn't even touching my mouse. It's rolled back as far as it could, and any attempt to move past that point automatically scrolls back.
Tried starting a new game and the issue impacts this as well. Issue persists after save/reload, exit/relaunch, and system reboot.
Issue is NOT impacting other Ren'py games or non-Ren'py programs, so I don't think it's a stuck input device.
Am about to try downloading the new version and seeing if that resolves it (was running previous build), but posting in case that doesn't resolve the issue.
Update: Fresh install did not resolve issue, but did break save. Also tried unplugging/replugging input devices, without success. Game appears to be unplayable.
Second update: A full purge of the game from my system including saves and reinstalling managed to resolve the issue.