as you have two profiles, can I give you two "solutions" to try. I am trying to work out if one is a manifestation of the other.

in one follow the instructions in "Rebuilding the Global Database" https://support.mozilla.org/en-US/kb/rebuilding-global-database

in the other follow the instructions under downgrade protection here https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html

The first I am about 99% sure will fix the issue. The second not so much, but if it does not the first will still work.

Please tell me how you get on. I want to test, because the first works for some issues and it really should not. Deleting what amounts to meta data should not make the program run correctly so I am playing with alternative options. Probably unsuccessfully.

PS I have never actually had the issue to test for myself.

Many thanks for the reply. The first solution - deleting global-messages-db.sqlite - fixed it. I almost did that before I posted the question, but being a cautious type I changed the extension to .backupsqlite rather than deleting it, and that did not work.

changing the extension "should" have had the same result as deleting the file. Unless Thunderbird was still active in the windows task manager. The existence or otherwise of a user windows is not evidence the program has shut down. Hanging on shut down is actually fairly common, not seen by the user. Caused by anti virus products in almost all cases.

Thanks very much! Deleting global-messages-db.sqlite also worked for me. But I hope the developers of thunderbird wil warn in future when they make an update with an effect like this. I read somewhere on the internet that the update only worked with the profile that was last used. I didn't have the time to attend to it sooner and I hoped they would solve the problem. In the meantime I used another email program, but I was worried about my adress book and archive. I'm glad to have it back now and more cautious.