I have been a long-time user. Have a iMac (OS 10.14.5) and Thunderbird 68.7.0. Suddenly, while reading a new message in the "Inbox," the message screen froze. I left the page to return to the subject panel. All the thousands of subject lines were intact, but would not show their associated messages. All my other folders, could be opened and everything (subject lines and messages were there and intact). I closed TB and rebooted the computer. Re-opened TB and all the same - i.e. all 4000 messages in the Inbox were gone, but subject lines still there, and all other folders seem intact. I then started getting new messages. They were all ok and still are, but all my old messages have vanished. I ran the "repair" program on this. It did not restore my messages, but instead it deleted all the 4000 subject lines too. What is going on? Is there any way to get my messages back? And is this a bug that will cause this to happen again?