Are you sure there's a tonal change and not just a volume change?
The FX loop should absolutely be set at 100% that's not debatable so there's something else going on.
Do you have the FX loop and B unit in and outs all set to the same Line/Instrument?
If the FX Loop Mix is set to 100% then latency won't be an issue, it sounds like you've got a parallel path somewhere.
Unplug the output from B and you should lose all signal, if not then it proves the parallel path.
@datacommando and many others have the patience of saints answering the same failed update questions time and time again while others just don't bother answering them anymore.
All the instructions are displayed in HXEdit and if for some reason the update fails, the recovery instructions are easily found in this forum without starting a new thread.
Cleckheaton was a whole different world to Tingley, we had to catch the bus to Bradford for the gig and missed the encore so we could catch the last bus home!
The Roaring Silence came out before the gig and was the reason we went but you're right about Bruce and Dylan and all the others that MMEB covered.
Yes that's true but I grew up listening to MMEB not Bruce Springsteen, I'm trying to think when I first heard Springsteen but it was a long time after my first ever gig!