So, I've managed to dodge the relatively common issue of cash registers losing their workers for about three years irl now, but it's finally happened to me. After the fall festival closed down and the winter one took its place, workers never came to man the registers on the festival lot. I thought it was odd, but didn't need them at that point so I didn't stress about it. But I just realized that the consignment store appears to be affected as well. I've never had to fix this issue before, is there a way to do it? Or is my save borked and I need to start over? My only hypothesis at this point is that somehow snow days are triggering the register workers to stay home, because every day I tried to shop it was snowing heavily(read: every day of winter it was snowing heavily).

Do you have the Shopping from Inventory mod? That one causes issues with manning the festival lots.

No, and everything was working with my current mod setup(some NRAAS stuff(not consigner) and Awesomemod) until winter hit.

The game automatically assigns new Sims to all of the Seasons food stands during an actual seasonal change, and could be trying to treat regular registers the same way. I know for a fact that the Sims currently manning all of the festival lot food stands (as well as the food stands I've added with seasonal lot markers to other lots) are NOT the same ones that were manning those same stands during the previous season. I also noticed that some -- but not all -- of the registers and professional bars had staffing changes as well.

I'm currently running Twallan's Register and Story Progression, so I know that it can sometimes take some time for all the registers/stands to be populated the first time in a new town. The same thing is likely happening during the seasonal change. I noticed that Register still showed a Sim associated with some registers/stands but that the Sim just never showed up for work. I might not have given Twallan's mods enough time to correct the issue, though. I noticed the problem relatively early, did a quick check for other vacant registers, and then simply unassociated those Sims. Within a few game minutes those same Sims were reassigned (some back to the same register/stand, while others swapped).