I have changed my audio interface A to B. Everything working fine except when I opened old projects, I receive a message dialogue “Audio interface A USB midi port unmapped” although I completely removed anything related to the old interface A. clicking cancel, removing the message dialogue and open the projects normally.
Opening new projects doesn’t have this problem.
I think that’s just an informational message to let you know that your old projects will need some editing, if you want to use external MIDI in or out for the tracks being listed.