Tough one to diagnose remotely. I can give you a few ideas to pursue:
Three daisy-chained MIDI devices is about the limit I would take. I don’t think that’s the problem here (if everything else H9 is working). But with any additional devices, consider a MIDI THRU box. That said, it’s good practice to eliminate the MIDI variables, and test out one controller with one device at a time.
I don’t have a DMC-6 here, but a MIDI Baby 3 would be similar. Do you have Zoia, Line 6, and H9 all receiving on the same MIDI Channel? Useful in some circumstances, but that can be the cause of some ‘cross-wired’ MIDI CC commands.
As for the H9, have you left the Parameter 1-10 MIDI CC assignments at defaults? As I recall, a stray MIDI CC#28 message might be resetting your PLAYMODE preset to an unwanted value / position. Have you noticed a change there?
The Disaster Area controllers are highly programmable, and can send just about any message. Lacking a MIDI monitor for diagnosis, I would think you can narrow down exactly what the DMC-6 is sending from their app (assuming it’s the same as the MIDI Baby 3 approach).