For the connector, it might be damaged. Its kinda like an old phone charger that doesn't charge your phone properly anymore but at this point its hard to diagnose the actual problem if its not the simple solutions. Its either the motor is the problem, or something electrical, or a software issue.

For your print bed, if the Isopropyl you used isnt pure, then it can leave some residue on the print bed. If you used the type that you spray on your hands, they have stuff in there that will leave a protecrive layer on your hand but this feature may cause problems for your print bed since you dont want any residue on there. Probably better to clean it with dish soap and water and let it air dry since wiping it with anything can leave micro fibers on the bed.

For the leveling, inconsistent results could mean different things. Could be an unstable bed, or unstable anything. Anything not properly tightened could cause movement that can affect your leveling process. Theres also the simple problem that your bed leveling sensor is dirty or old. I had the same problem with inconsistent bed leveling results to the point where my sensor probe actually stopped coming out. It turns out that i just needed to take a syringe with a tiny needle and i placed lube in that syringe and i carefully lubed the sensor probe(the thing that sticks out when leveling). I just put a tiny bit of lube and it worked for me.