I have the exact same issue with 2.91 on my HX Effects. The LED doesn't work correctly when a snapshot is assigned to FS4. The on/off state of the LEDs is correct for the other switches that have snapshots assigned to them, though they do not honor custom colors selected in HX Edit. I also have issues with a snapshot assigned to FS5 taking two taps to activate. It's weird that it's specific to certain switches, FS1-FS3 and FS6 seem to be ok other than the custom colors.