jerky-jerky mouse movement...

My iMac (Retina 5K, 27-inch, late 2015), 3.2GHz Quad-Core Intel Core i5, 24 GB 1867 MHz DDR3 RAM with the OS: Catalina OS version 10.15.3.

I mistakenly upgraded my Kensington wired Expert Mouse to their latest software (upgraded from, I believe, TrackballWorks v1.5.0 to the 'new-and-improved' KensingtonWorks 2.1.11). I wasn't sure if the problem started with the Mac OS upgrade to 10.15.3 or the Kensington upgrade to 2.1.11. Anyway, my experimentation entailed completely removing all things Kensington, then I re-booting. What remained was the native Apple Mouse Drivers. And things worked for a while. Then the mouse pointer began displaying that jerky-jerky, stutter motion again. I re-booted yet again and all was right with the world - for a while. Then the stutter motion started up yet again. It is doing this as I write this - and I am using the default Apple Mouse driver. I have even tried switching out the Expert Mouse altogether, replacing it with the original wired Apple Mouse...no joy. The connections are this: Apple Mouse to one of the side USB ports on the Apple Keyboard. The Apple keyboard is plugged into a rear-of-the-iMac USB port. I have tried unplugging everything from the back of the iMac, then reconnecting only the keyboard and mouse to the back of the iMac...good for a while (time always varies depending on the amount of usage). If left 'un-booted', then it gets so bad that sometimes the pointer will not move at all for2-3 seconds, then 'catch up'. Is there something being slowly corrupted in my OS 10.15.3?