contacts keep disappearing on S5 after 5.1.1

[lynstks]

Now my contacts disappear regularly from my S5. I can get them back only by restarting the phone. Error messages says ....android.acore has stopped. I'm running 5.1.1, and I can't haven't been able to tie the problem to any specific app.
I cleared the cache and did a factory reset a few weeks ago because my "back" and "menu" buttons weren't working. (They are still not working, but a separate app has given me a serviceable "back" button.) I cleared the cache again this week, but the contacts still disappear once or twice a day.
Any ideas?

 

[B. Diddy]

This can be tough to troubleshoot, since it can be caused by several different things. If you search this forum for "acore," you'll find lots of threads. The common thread seems to be contacts, though. Here's one possible solution: A solution to one cause of android.process.acore stopped working