Just making sure you’re not using the 9v and 12V jacks that are right next to each other on the 4×4? you have to pick one. from the manual: Note: The 9V and 12V outputs within a pair are not isolated from each other (their negative terminals are common). It is preferred to use only one from each pair. If using both, combined output should not exceed 400mA.
i seems to me you might need more power for 2-H9s, a timeline and your switcher.
also, i found that sometimes on midi devices using the midi thru option is not optimal. sometimes the signal info can get messed up. i was having weird midi things happen using my Boss ES-8 switcher with 4 midi devices daisy chained. i just recently started using a midi soultions quadra thru. all good now. but i would start with your power first and see if your issues go away. hope this helps.