Sometimes I can’t understand how some basic bugs are not reported (and not fixed).
There is a bug in Unity 2019 LTS editor (Inspector window) I have noticed in Unity 2018 LTS also:
Without any reason, the selected gameobjects are not showed in the Inspector anymore…
The solution? Close Unity and reopen.
Are you perhaps locking the inspector window by accident?
Have you considered reporting them yourself?
Of course, I checked the inspector is not locked. 