Issues with MIDI MuRF passing signal while connected to MIDI cable

I’m using my MF-105M MIDI MuRF to reamp a clean korg MS-20 track within Pro Tools and I’m dealing with a strange issue: the unit will pass signal and affect signal when recording to Pro Tools and not synced to MIDI, but when I sync it to MIDI (specifically, when I have connected the MIDI cable from my interface to the unit) the drive and rate indicator lights turn off and the unit stops passing signal as soon as I start recording.

any ideas? I’ve never encountered a problem like this with a pedal that has MIDI capability before. thank you!