Sims Pausing Tasks/Delaying Starting a Task

Has anyone else noticed that sometimes when you have a sim start a task, it pauses? 

Once, during a simchase, I had a task that required multiple sims do hours long tasks at the exact same time. One of my sims, for whatever reason, paused at some point, and I had to use social points for her to finish at the same time as the other sims, despite starting them all at once.  I know if some of your sims are inspired, they do things quicker, but this was not that- she was hours behind, as if she had never actually started the task.

Last night, I put one couple to bed, and when I got up this morning, one of them still had 6 hours and 9 minutes left of his 6 hours and 30 minutes of sleep. Why does this keep happening?