Galaxy forgetting contacts!

[CanAm]

My Galaxy S3 Neo recently managed to forget a small number of contacts (unfortunately among my most used numbers).

When I re-added them they disappeared again within 12 hours, and definitely overnight, even thought the phone is left on. I also tried editing unused contacts to show the details of the missing contacts, but they also disappeared!
I did edit one contact to add a missing surname and this one is fine.

Any ideas?

[CanAm]

In case anyone else has the same problem I contacted the Samsung Helpdesk who suggested clearing the Contacts and Contacts Storage caches; this made no difference!

So I updated and reinstated all the corrupted and missing contacts and immediately restarted the phone. This saved all the alterations and any subsequent changes have also saved as normal.