Recently, I've been getting "unexpected EOF" errors when opening some mails. Here is a recent one from the mailing list which produces this error for me: https://gist.github.com/d6fd24d401bd846524723401aa87160e . It had been synced using isymc (mbsync) to a local folder.
I'm using version 0.5.2 on archlinux.
When replying to a message, it is not marked as replied to.
When archiving mails from a large maildir, cpu usage goes up to 100%. Especially when archiving several mails at once.
I don't know what more information I could give, let me know if you need more specification.