To this day this is still an issue that makes it pretty annoying to use Mailspring and honestly makes it hard to recommend as well.
Another bug report from December mentions the same issue as well: Every time I open this email client there's new crap to deal with. Such a frustrating software
I don’t understand how this is not a more widespread issue. This used to happen randomly every couple of months a while ago with my very simple IMAP/SMTP account. Now that I’m in a period where I rarely open up my laptop and it has to sync a lot of emails at once (maybe unrelated but this is just what I’m observing anyway) it happens pretty much every time, which means it’s practically unusable for me sadly since I have to completely reset Mailspring every time I want to use it.