Keyboard letters stop working

Today letters ‘C’ and ‘H’ and others stopped working. Even pasting them from the pass through computer deleted those letters. Disabling and re-enabling the keyboard didn’t work. Disconnecting and re connecting didn’t work. Virtual keyboard didn’t work.

Eventually is restarted working, perhaps due to one of the above interventions, but it wasn’t immediate. It happened to be before, wondering if we can pinpoint the issue?

It might be that the KVM is stuck, with keys like Ctrl or Alt being continuously recognized as pressed. I suggest you use the “bad link mode”.

How do I use bad link mode?