It seems I've stumbled into the solution to this problem, which apparently has been self inflicted. Out of curiosity, I did also try to load the save file from a different slot, but that also didn't work.
When I finally resigned myself to having to re-download the game again, it suddenly occurred to me that I had ran into the bug (was/is it a bug? only a few people seem to have it) other people brought up when they need to meet Serena in the living room at some point. This prompted me to search this thread for similar issues and to hopefully find a solution, when I ran across this post (
https://f95zone.to/threads/greener-pastures-v0-9-arcaos.80656/page-12#post-6834365) which offered a solution, allegedly pulled from discord. In my blind eagerness to resume my playthrough, I completely failed to notice the post was made about 3 months ago, which would make the file obsolete in this version of the game, I imagine. Although to be fair, it did seemingly fix the problem and allowed me to continue...
Today's problem was fixed by simply restoring the original file which I backed up in case something like this happened. I just wish I remembered it sooner, before bringing this up here and spending a couple of hours trying to fix something I broke myself. I couldn't help but facepalm so hard that it caused the cat to jump higher than I've ever seen him jump and quickly flee the room.
At least, if nothing else, I hope my brain fart helps people who go through the same issue. Or prevents them from having the issue in the first place.