I can't help with the OP's particular problem with Thunderbird but I had my own issues a year or two ago when I used XP - I got a lot of suggestions from PPRuNers some good and a few less so!
Since moving to Win 7 and a variant of Gmail I stuck with Thunderbird but am getting problems again - new and sillier ones now. I moved from Firefox to PaleMoon about a year ago - it's not obviously so different but I prefer it for reasons not all directly related to its functioning - and this has prompted me to think about FossaMail which is something akin to a cousin of PaleMoon. Do any of you have experience of FossaMail and what can you advise about it, please? It may be my age but I want to continue with an e-mail client rather than accessing my Gmail variant through my browser.
It might interest the OP too if it turns out to be steadier than Thunderbird seems to have become....