Try connecting your guitar to input 1 and coming out 1&2 in stereo directly to your Iridium. Do you still notice a problem? For testing purposes, just start out with THRU utility algorithms or bypass any presets in Path 1.

Do the same connecting the guitar to input 3 and coming out 3&4 n stereo directly to your Iridium. Anything issues? Same thing, for testing purposes, just start out with THRU utility algorithms or bypass any presets in Path 2.

This isolates both paths of the H90 to send if it is in fact an H90-related issue.