I updated MP to the latest 1.3.75, and I’ve updated Ubuntu to 21.04. (Yeah, two updates at once… I should know better)
When I tried to plan a mission, rather than displaying yellow lines from one WP to the next, it creates a yellow rectangle using the two WP as corners. In the image you can see there are only three waypoints and a home point. But the yellow box makes it unusable.
I have my ADS-B feed on the data page, and if I check the info on a plane nearby, rather than a light blue line between the plane icon and the text box, there is a blue square.
Just an update, I did see the other thread that had the same issue (Graphical problem on ubuntu Hirsute with mono) but my issue never went away. I had done a few updates of Ubuntu since then, and updated MP and the problem remained. Until today: I changed my desktop to the Ubuntu Budgie 21.10 and that fixed the problem. Suggests to me the problem is something to do with the desktop environment and how it interfaces with MP. Anyhow, I’m just happy to have it all working again.