Running diagnostics stays stuck on "Diagnosing..." screen

I run "diagnose and feedback" from the menu.

I expect to know what's going on.

(In that specific case: I tried to reset D4M to factory defaults to scrap some disk space, and it failed telling me "there was a problem.")

The diagnostic screen opens. Then in the black rectangle it just says "Diagnosing..." but stays there forever (waited 10 minutes).

This was just after trying to reset D4M to factory defaults. After that, my D4M install seems to be broken (will open separate issue about that).

Can't reproduce: now the diagnostics screen tell me something else.

display what's going on in real time
or give instructions about what to do if things time out (I got a magic command a while ago to run the diagnostics from the console but can't find it anymore)
detect when diagnostics take too long?

Provide feedback