New Skill Day not working properly for large household

I have a household of eight sims. I realised that it was New Skill Day when one of them got the moodlet for having increased a skill on New Skill Day, because the holiday pop-up still isn't working for New Skill Day the way it does for all other holidays.

I took the household to the gym to build fitness skill. Eight sim hours and several skill levels later, only two had the yellow highlight for having completed the holiday. The other six hadn't completed the holiday, despite gaining several skill levels.

I wondered if this was a bug that each skill could only be counted for one sim for the holiday - I had one who gained skill tending the garden in the morning, which was what alerted me to the holiday without the popup that is still broken, and then only one of the other seven completed the holiday at the gym. So I took the remaining six household members to Casbah; I set three of them to learning the three different musical instruments there and the other three painting. All of them completed the holiday when they got to level 2 of the relevant skill, so it's not a matter of each skill only counting for one sim.

As far as I can deduce, it's just broken. I would like someone to fix it, please. The holiday pop-up needs to appear the same as it does for all other holidays, and it really needs to work for every sim in the household on the first skill that sim levels up.

Never mods or CC, playing on PC. Lots of packs, but I don't see how that would affect the problem with the holiday.