Since the mirror raises, it is likely a problem in the lens. Trying another lens would be a good way to isolate the problem as to body or lens. That's one reason I have about 2.5 SQ-A kits on hand! The shutter, and a bunch of mechanics are in the lens, so it could be cleaning and lube time. But there are also some electrical connections in the lens that could have a problem.
There is some Bronica info at Buona Luce ("good light"!) that might provide some insight.