This is a strange one, as it doesn't always happen, just in some unknown circumstances. With a certain sequence of clicking midi learn, delete and some order of trying to chose the type, channel or number first, the type field is displayed empty (no cc/note entries) and selecting a channel then just does nothing.

The workaround in that case is to navigate back out of the midi config and restart it.

When i was trying to reproduce this misbehaviour, it didn't happen, but it did happen a few times before, so i'm not sure what exact sequence of events or inputs causes it, sorry.