Eclipse: Hover broken in debug perspective

I had this problem too once, I "just" had to restart eclipse, after that the hover mechanism worked again.

I went to Window - Preferences - Java - Editor - Hovers, hit "Restore Defaults" and "Apply" and that fixed it for me, even though nothing actually changed in the settings...

Go to Window - Preferences - Java - Editor - Hovers.

1. Is "Combined Hover" selected? Uncheck it; apply; close the window; restart debugging session; go back; check it again; apply.
2. If the above doesn't help, you can check "Variable Values" option and specify a modifier key for it. Not as convenient as "combined", but should work.