1) Arrange applications in a layout
2) Expect that the layout will be there on next login
3) Do a REBOOT
4) Session / layout appears to not be remembered
5) Restores some previous layout
*) To save / remember the layout it's currently required to LOGOUT.
#) It should remember / save it on reboot too.
Note: I reboot using 'sudo reboot'
I'm on Plasma 5.17.2
This somewhat/partially/mostly works in Plasma 5.20 on X11 with KDE apps that support it. In the future it will be possible to do it generically on Wayland via Bug 15329.
*** This bug has been marked as a duplicate of bug 15329 ***