Thunderbird under Debian 11 gave minor miscellaneous problems from time to time. But when Thunderbird lost a couple of messages, I switched to Evolution. Now I have no more problems and I prefer the features Evolution; I wish I had discovered Evolution long ago.
-- He turneth rivers into a wilderness, and the watersprings into dry ground; a fruitful land into barrenness, for the wickedness of them that dwell therein. - Psalm 107:33-34