Ideas
With the release of the latest DLC and the most recent update, this problem has been happening to me very frequently. Most of the time it resolves itself, but now it has reached absurd levels. Upon the active household returning to their home lot, the in-game time has frozen.
Right before the bug occurred, the game was set to the third simulation speed (one Sim went to sleep, and the other started painting). When pausing the game or switching to build mode, character animations and the day/night cycle outside continue to play.
After waiting for 10 minutes, I decided to exit the game, but out of habit, I clicked "Save." I have now been looking at the saving screen for 20 minutes, while the character animations and the outdoor time of day continue to change.