My tiny poor little 4B-SST² when new was a pita to get t ostart up until I had fiddled with the remote power on, flipping switches in every way possible. THEN KABOOM it turned on.
Ever since I am very careful to always use the correct set of turn off pre (to remote turn off amp) then front amp switch, the rear.
I say this thinking maybe your remote turn on has shorted or ??
Have you checked the remote turn on wires. Swapped them from on 28 to the other?
Just a thought.