I can't find the original post but, its happened again. I watched 4 ads in a row and didn't get anything or extra coins like i normally would get after completing an event. It was working fine eariler until the app crashed for some reason. After that, it wouldn't give me rewards after watching ads.
Oh there is probably a post somewhere about this. But it sounds like a bug to me.
Could you post a bug report for the issue? https://answers.ea.com/t5/Bug-Reports/bd-p/the-sims-mobile-bug-reports-en