355 Wiring diagram

There really isn't anything electrical that would stop the roof going down if the primary rams have already started operating, especially if the pump is still running. If there was an issue, say, with the primary ram internal microswitches (S1 and S3) triggering prematurely, the pump should stop running.

It's either something mechanical or hydraulic. Maybe fluid going somewhere it shouldn't.

I have seen bent piston rods before, stopping movement, but only at the retract end.

Hopefully there is nothing wrong with the pressure relief valves in the pump block.

When you put the roof up, does the front part of the roof start extending immediately (rather than waiting for the primary rams to extend)? I'm just wondering if fluid is being diverted into the wrong part of the system.