Facebook Messenger conversations disappeared

Hello
My husband has an extensive conversation history on Messenger with both our daughter and me. The other day he shared an image from Pinterest via Messenger with us both. Now all his past conversations with our daughter and me have disappeared. Only the most recent response from each of us to him remains. I've checked his other contacts and the full conversation history with them is still there. I've virus scanned his phone, updated the phone software, Messenger and Facebook, and restarted the phone. I'm at a loss. Can anyone tell me how to get the conversations back please?