I, too, have this issue with my Mark V 25.
I specifically got the Helix because it supported the amp switching.
I really don't see what the issue could be, as the Mesa amps are a very simple short-to-sleeve switch. Can someone from Line 6 describe exactly how the remote switching port operates?
I am willing to wait for a fix, but if this drags out for months and then we find out that it is unfixable, can Line 6 confirm that they will offer full refunds?