I have the same issue. On their current home lot, my sim will be in the middle of a task and when i go to 3x triple speed, the clock freezes and everything gets stuck on 3x speed and continues animation. The UI becomes mostly unresponsive except for Options menu, Events menu, and Build mode. I haven't tried to enter Manage Worlds in this state in case of real crash. The animation continues even if I enter Build mode in this state, which is weird to see haha.
It usually just resolves itself and goes back to normal after about a minute or so. It also causes the task to remain in queue without progress/completing, so when it lets me regain control, I just shift click my sim to reset it, and it's fine! so not that big of a deal I guess. For example, last time it happened when I was just giving dog a bath and he was still stinky afterwards :(
This only happens on their current home lot after I've been playing for an hour or so, specifically in the corner where I display many wall shelves full of crafted items and collectibles (coincidence? maybe).
I read somewhere that it may be tied to the lot itself and to try Evicting the sim and move them back in, so I will try that today, and it it doesn't work I'll save the lot my gallery so I can bulldoze the lot and place it again to see if that resolves it. Kinda hard to catch it if its only sometimes.