I'm sorry if this post is against the rules, I just couldn't find anything else about it!
After installing Generations, on some days, after receiving the carpool pop-up, the carpool won't even show up for a certain sim. Then, when I tell them to go to work, it says it's not their work hours when clearly it is, and on the bottom it says they have work in 1 day or so when they should be there already. I haven't told any of them to take paid time off, and it get's obnoxious because they only end up working 1-3 days a week sometimes. Has anyone else had this problem with Generations?

Yeah, the pop-up saying the carpool will come in an hour lies. Did your sim just get married, have a baby, notice they are pregnant or move to a new home? All these cause automatic days off but the popup still comes. I only noticed it since Seasons, but it might be a Gen bug.

These are separate problems, but the OP's is definitely the more irksome. It just seems like the work schedule glitches once in a while, because there really aren't valid reasons connected to it, like you suggest, Sirah (the one you're mentioning, you're right, that's from Seasons).

I don't know how to solve the actual problem, but it might be helpful if you add some mods that reduce the number of days off from legitimate events, like the just married, moved in, or the ridiculous amount of maternity leave. Or even make your sims work on the seasonal holidays with...I'm pretty sure it's MasterController.

I wish I had better advice than work around it, but that's pretty much what I do about it.

Thanks for all the advice! Actually, I downloaded Razer Game Booster as my laptop isn't that great, and the issue seems to have resolved itself, thankfully. The only thing that wasn't solved is that one of my sims won't go to work unless I make him change into his career outfit, and has ended up late to work or has missed it entirely xD. He's about to retire soon though, and I hope it won't be a problem in the future.