I'm not sure if you ever used any mods on your old save but there are some out there that can definitely mess up your game calendar and holidays so be careful if you ever decide to use them. Start a fresh no-mod/no-CC New Game and test to see if everything is working properly now. Re-download the pack and you should see it again in your Sims 4 Packs folder. All the towns in The Sims 4 now have the weather that corresponds to actual cities, like Newcrest now will have the weather similar to Vancouver in Canada. If you trash your Seasons folder this should prompt Origin to notify you it is available for download. Oh, that is the coolest mod The Weather Realism Overhaul adds visual changes to the weather, makes wrong forecasts, and the weather will be more accurate to our world. Here is a link with detailed instructions on how to do this: You can try triggering a re-download of your Seasons pack to replace the files and this might correct your error. There is another way you can try it though.

The game repair function through Origin will check your base game plus all of your game packs if you were on a PC, but for Mac users like you it only checks the base game. This mod is designed with the same realistic experience. Whereas in real life, weather change naturally. For example, if in normal days the forecast says it’s cloudy, then it will stay cloudy. The mod brings more realism in the game in terms of weather and event forecasting. I missed the detail in an earlier post that you are playing on a Mac. One of the best sims 4 cc seasons mod is the weather overhaul.

Sims 4 weather mod