I am running with ubuntu 18.04.3 and thunderbird 68.2.2 (64-bit) In my list in the email inbox I seem to be getting a lot of blank lines. They seem to tend to come and go. Sometimes I can click on them to see the content, sometimes not, sometimes I can delete them sometimes not, its all pretty strange. I can also click on compact folders and that gets rid of them too, sometimes. I can also usually (not always) deal with them by restarting the program. I wish I could be more specific but this is an odd one.