Can you describe how you’re hooking them up? If you are daisy-chaining the pedals, did you make sure to configure the MIDI OUT of the first H9 to “THRU” in the system settings?
Did you also configure your DMC controller to work for three pedals? I believe Disaster Area defines them as DevA, DevB, and DevC. Then you must go into each device and define which pedal it pertains to. For example, DevA – TimeLine, DevB – H9, DevC – H9#2. These types are preprogrammed by Disaster Area from factory but you still have tell the controller which “pedal” belongs to each “Device.” Also, each pedal in your rig has to be assigned it’s own MIDI channel. Whatever pedal is assigned to DevA should be programmed to MIDI channel 1, DevB should be MIDI a channel 2, DevC should be 3.
Page 4 & 5 of the DMC a manual goes into specifics: https://static1.squarespace.com/static/5ffa32e2e3802f025d87246d/t/60b156a5256b153d1e64db3e/1622234789413/DMC-3XL+Gen3+Manual+v1.60.pdf