Not sure what is going on, then. It works as expected here: version 18.104.22.168. Tested using a MIDI Baby 3, Source Audio Reflex; I expect the FCB-1010 here, or CC#0 via DAW Transmit will yield the same results.
I even tested Aux switches to see if they might diverge from MIDI; as they have mirrored parameters in Global Mapping. Works the same.
Unfortunately, there is no Learn function in Global Mapping, like there is with individual parameter control. Makes for a great test to confirm what you’re sending is getting received by the H90.
You could try sending CC#0 to (any) parameter, using Learn, to see what happens there. Without narrowing down the range, you should see (any) parameter snap between minimum & maximum values.
Better still, a MIDI Monitor would give you back exact CC Number & Values at a glance.