Ajax156, interesting info that I'm not alone with this problem (maybe not the same, my cam FW doesn't freeze) but unfortunatelly we still don't know the cause. It's positive, that at least in your case, the issue was temporal. Just to be sure, your mirror problem started just after you replaced the solenoid and has gone when you opened and assembled it again?
Please can you make a simple test:
1) with unmounted lens turn on the cam in bulb mode
2) press and hold the shutter
3) after the mirrot lifts and aperture lever moves up try gently pull the lever down with a tweezer on small screwdriver, stop pull when you feel some resistance
How it moves? In my case I can pull it very softly down to default position (one half), when i release the lever it moves up via som spring, not much fast.
Just want to see if it behave same or differently.
BTW didn't you used this quick hack:
https://www.pentaxforums.com/forums/attachments/58-troubleshooting-beginner-...-objektivu.jpg before repair? If it may have some coincidence with mirror problem...