Sorry, this doesn’t help in relation to your issues but a lot of users left Mailspring as this software was pretty much abandoned a long time ago now and almost all of its users were experiencing bugs in some shape or form…
See here. I posted this back in June… So almost 6 months ago now.
Unless someone with the necessary development expertise with what this software is built-in contributes and forks the project, it’s unlikely to get better any time soon. Make of that what you will of course…