If you click on one of the “Failed while executing…” error messages in your GUI is a detailed error message shown?
The “Error in updater” messages are making me wonder if you’re running into this issue (which basically boils down to mono having out of date SSL certificates which an install of ca-certificates-mono seems to resolve):
Out of curiosity, if you go to “System Info” on the “About” page, what MonoVersion do you see listed?