Why does my Moto G 3rd generation keep losing some of my contacts?

[AC Question]

Some weeks ago, the names on some of my text messages disappeared, only showing the numbers. I have tried several times to save the names again by updating my contacts on the phone, but the names appear for maybe a few minutes or hours and then disappear again. I have tried having synching switched both off and on and it happens regardless. Some of the contacts have remained in my contact list but are still not showing on the texts, and some of the contacts I have added recently have completely disappeared from my contact list. When I check my contacts on my computer in Outlook, all the info seems to be there. This all seems to be completely random and I have no idea how to fix it - any help gratefully received !