Since some days/weeks (?) I get this:
First the updates are displayed without issue but after applying them I get a void window and finally this void window for achieved process.
Is this known or should I report? Am I alone to experience this issue?
Nope you’re not the only one — Had similar empty box, for the past several days when using Software Update Manager. So, I resorted to using command line and apt directly. It disappeared when I removed everything gnome related in my home directory. Something was corrupted in my home directory, but I’m not sure if it’s the same issue as yours. You may wish to file a bug — I was running XWayland when it happened.
Mmh, I run a Wayland session too. I’ll report this these days.