when you remove the screw to the main shaft, it release tension on the shaft which has a centering mechanism (see photo below). I posted the picture its the white post on the left side. When you removed the screw, you may not have placed the main shaft correctly back before re-tightening the main screw. you can try to loosen the main screw slightly push the knob in, jiggle it slightly, pull out and tighten again. those gears inside are very small it wouldn't take much for you to get them off calibration so the electronic switch inside doesn't work. You may be off by one or two teeth.
it's hard because you are working 'blind" unless you open everything up. Try adjusting slightly backwards and then tighten the screw.
can you post a video showing the "loose" knob? Can you post a pic of your replacement knob?
If you don't fix the loose knob issue it will never work because the knob and shaft must be tight in order for the white cam and gears to engage the switch correctly.
Hope this helps