I just have to throw this out there. I’ve owned several pedals that dropped volume even when off. And true bypass is not a guarantee of unity volume...it depends on the build. If you plug a known patch cable that measures less than 1 ohm at DC on both the center and shield into the loop and don’t hear a volume drop, it’s the pedals/board. But some very low impedance cables change with frequency and this can make for a perceived overall volume drop. Also Marshall knows their loops (and almost everyone else) have a minute change in tone, probably due to a change in input impedance loading individual pedal choices differently. This is why they have a bypass switch. Wanna hear a crazy tonal affect from input impedance? Try putting a modern digital pedal before a vintage tone-bender. It’s pretty much unplayable.