Mail app email body text disappears when scrolling or viewing emails

Hi, I've got a problem with reading my emails. Everything loads okay at first and I don't lose mails, but as I scroll down if there is a number in the thread, or just check a number of mails, the main body of the text disappears. I then have to close down mail and then re-open it to get back to the email I was reading. I've tried rebuilding the mailbox and it makes no difference. The software is up to date but I haven't been able to fix this. Any advice to sort out this annoying problem?