Hey, sorry for the late reply - I had covid and things have been a bit sketchy. Although my problems stopped short of the amp actually cutting out, I did find a solution, albeit an expensive one. I bought a new second hand amp, the same MB combo (am I crazy?). I had it shipped to my bandmate's house in Birmingham (we do most of our gigs in the Midlands), used it at a gig last month and it was great. Amp no.1 is playing nicely at the moment for practice - if it starts getting crotchety again I turn all the knobs back and forth several times, and that gets rid of any unwanted crackling. I also have it sitting on a chair for added clarity when practicing. I don't know if that's that helpful to you really... Maybe I should have been twice shy after being bitten, but I love the MB sound - to me it is a wonderful blank canvas.
Did you get yours back from Essex Amps, and if so what was their verdict?