so, it turns out I wasn't using wayland anyway.
my server started it's life on mythbuntu and at some point I moved to the mate desktop but, as I only use it as server, I forgot it was using X11.
I removed all wayland libraries I could - there are 5 that I can't seem to be able to remove without losing my whole desktop. It didn't solve the issue with calibre hanging after closing.
Any idea what library might be causing the problem? I installed it and always upgrade with "sudo -v && wget -nv -O-
https://download.calibre-ebook.com/linux-installer.sh | sudo sh /dev/stdin"