Why has my message disappeared on only one contact

[iMore Question]

After the update iOS 10, one contact that I had several messages from has disappeared. All my other messages are still there. When I try to go back to older messages on that one contact it goes back to different times of day each time but only to the day before. I have other contacts that go back before the update & they are still there just one contact seems to be messed up. Please help!