When leaving my SQL-developer open over nigth, my connections become invisible. The connections are still open and available but unfortunately invisible.
I have to re-start SQL-developer in order to fix this annoying problem.
I don't know the exact reason for this, Maybee a shutdown of a database or something else.
I'm experiencing the same issue as KarstenH-dk -- connection window is blank... try to close, reopen window, connections don't reappear -- have to close EA4 and restart EA4 for them to show back up