If you opt to reinstate the plasma-x11-session and if you have previously switched to the new plasma-login-manager, it might be advisable to revert to sddm as well – I believe PLM is optimised for Wayland and is not strictly compatible with X11 – though I have not been following it closely, since I no longer use X11.
Keep in mind that KDE support for X11 may now be limited; the option will be removed completely in the near future, just as GNOME has already done.
The “pageflip” issue has raised it’s ugly head for a handful of users, that I’m aware of, but there doesn’t seem to be a definitive resolution at this time. If you search the forum for “pageflip” or “page flip”, you will likely find a few relevant topics – one in particular shares a few links to information that at least seems promising.
Nonetheless, if you wish to switch to using X11 in the meantime, I believe Manjaro XFCE remains fully supportive of X11. There are also other possibilities, including a few unofficial Spins:
See also: