I also got the same behaviour when I changed a patch from my Prophet 12. It sends CC#32 with low values (0- 7) when patch up or down button is pressed. On H9, there’s default mappings for input volume which happen to be that same CC#32 and that’s why H9 “mutes” itself when patch is changed. Don’t know why activating preset on H9 does this too, but it does.
When I tried to change volume cc mappings from the H9 Control software, I found there’s a bug in it. Input or output volume cc mappings doesn’t really change to no mapping when it’s selected from the selection bar at the first time. And assigned CCs are shown randomly on both input and output volume “setting bar”. Sometimes there is nothing and some time there’s cc which is really assigned to it. And even when there’s assigned CC shown on the “setting bar”, there’s “no assigned” selected on the selection bar when trying to change the mapping.
Now to the fix:
I got it working by removing both input and output volume mappings. Due to H9 Control software bug, I first assigned CC127 to both volumes and then changed them to no mapping. Now I can change patch from Prophet 12 or activate preset on H9, and it doesn’t mute the input volume.