

I’ve literally never heard of Bodhi Linux, but apparently it is a fork of Ubuntu LTS, which will have very outdated packages if that is a concern for you.
AntiX is likewise a fork of Debian Stable, so I suspect it will have the same issue. It also does not use the more standard systemd init system, so finding support could be an issue.
I don’t think that it make sense to start off on such obscure distros. The advantage of a widely-used distro is that there will be forum threads and a much larger network of support to help you learn and debug issues.
I can’t really speak to the security aspects of either X11 or Wayland.
I have been using KDE on Arch across several machines for about 3 years now, then Manjaro for a year before that. At no point have I experienced instability or issues like that. Especially that last one; I’m the sort of person who regularly has 10+ tabs open on laptops with a fraction the amount of RAM that you have.
I would say that is definitely not normal. If that happened to me, I might search online or check
journalctl -b -p 3
to see if it yields any clues.