Comment 2 for bug 1807197

Thank you for your bug report, I can't confirm the issue on a new bionic installation
- log into the normal session
- log out
- click of the session selector, 'ubuntu' is selected, pick 'ubuntu wayland'
- log in
- reboot from the top right indicator
- select the same user and click on the session selector
-> the wayland session is still selected

Could you include your journalctl log from the session having the issue? Best if you enable debug in /etc/gdm3/custom.conf and reboot so it includes more details

When you log into the other session can you look what XSession is included in /var/lib/AccountsService/users/<username>?