Hi,
The core issue here is likely that most modern desktop environments don’t handle running multiple sessions as the same user very well. This is likely to be aggravated by the fact that one of the sessions is X11, and the other Wayland. One option might be to have two separate users, one for remote access via ThinLinc, and one for local console access.
Are you trying to access the local console session on your Ubuntu machine remotely? ThinLinc is a terminal server solution, so this isn’t actually a use-case we explicitly cater to. ThinLinc creates its own sessions, and is designed for multi-user systems. One way of handling this though is to connect via ThinLinc, even when sitting in front of the physical server. There’s a bit of discussion around this here:
Hope that helps!