I once had such “funny slew stuff” suddenly happening with my Keypad and AP-1200 – but with a new CP4, a few years ago.
The previous old CP3 worked perfectly when hooked back up to either mount with the same cables.
I even made up a small circuit board with toggle DIP-switches to test slews using only the mount’s manual Guider Port, taking the keypad, APCC, and PC ASCOM driver out of the possible causes.
Then Howard logged into my system via TeamViewer, and monitored what was going on in the CP4’s firmware, using his Remote Terminal app, for simple offline diagnostics, as we talked on the phone and I went through my switch toggles.
Howard, as usual, very quickly discovered a possible cause of the firmware having suffered from latent static, or X-Ray scanning damage during CP4 shipment, which may have zapped or weakened the IC, somehow, even encased in the aluminum cover.
Simple repair after that.
Might be worth eventually doing the same AP remote examination of your system. An expert’s pair of eyes, and skilled background, would surely help find you a quick solution, provided you have a repeatable test procedure.