[Evolution] Unable to retrieve message

[Jonathan Ryshpan <jonrysh pacbell net>]

I've been getting results like this fairly frequently from evolution; when attempting to read a message (double clicking on it in the message list) a notice like this appears:

Unable to retrieve message.

Cannot get message 1578599196.1398_1004.amito from folder /home/jonrysh/.local/share/evolution/mail/local/.nancy: No such file or directory

This is not surprising, since the file 

/home/jonrysh/.local/share/evolution/mail/local/.nancy/1578599196.1398_1004.amito

does not exist. However the file

/home/jonrysh/.local/share/evolution/mail/local/.nancy/cur/1578599196.1398_1004.amito:2,S

does exist and contains what should be displayed. Evidently something is wrong with the index.  I had displayed the message about 5 minutes earlier, before a reboot. The problem usually disappears after a while. Can anyone tell me what's going on, how to investigate it, how to prevent it, or how to recover?

System is Fedora-31

KDE-5.17 (I think)

evolution-3.34.2-1.fc31

Thanks - jon