MIDI outputs 'missing' since Sierra update.

On my Pro 9 system, since updating to Sierra several hitherto reliable MIDI ports (for external hardware synths) have stopped working and can’t be replaced. The Audio connection with my outboard interface (Presonus FireStudio) works fine.
I suspect this is due to driver issues from an ancient auxiliary MIDI interface (Edirol UM-2EX) I have been using, but it worked fine for the first few days after the update.
On checking MIDI functionality via the Mac Audio MIDI settings app, I find that only direct connections from the audio interface’s MIDI sockets work on the app – there doesn’t seem to be any MIDI transmission between the Mac Mini and interface over Firewire.
I have tried various solutions involving reinstalling the driver, deleting plist files etc., but these are so time-consuming that I’m reluctant to bother unless success is fairly certain.
Do earlier Cubase versions contaminate the latest version? I have files from three earlier versions of Cubase on my machine.
By the way, I’m not sure yet whther Cubase is at fault here, and I’m very happy with Cubase Pro 9 on the whole.