Make sure you have the correct connections. Some people don’t realize input and outputs are on opposite sides of the H90, not stacked above each other; a common mistake.
H90 Out 3 to Input 1 on H9
H90 Out 4 to Input 2 on H9
H9 Out 1 to Input 3 on H90
H9 Out 2 to Input 4 on H90
