After much experimentation ...
I was using a generic hard case on the phone vs. a Fosmon case & the issues eventually re-surfaced. The screen appeared to be hyper sensitive - sometimes I simply hovered over a screen item & registered a touch. Cortana would fire randomely (like Hey Cortana, ready for speech input). Touch would be unresponsive, fixed by locking & unlocking. I uninstalled Glance Background early on in the process, tried show picture OFF & ON in Lock Screen. I uninstalled Gestures Beta as that might have caused the problem. I was using the device naked & still having problems.
Finally, my issues appear to be caused by Start Perfect (an app), which I used to add transparent blanks to the screen. I hovered over one of the blanks & the screen freaked. Next time, I clicked on one of the blanks & a black screen appeared, then freaked, when I closed it (used the X). I've removed the blanks (spacers) & all appears to be normal for the last 5 days w the Fosmon case (did I mention I like that case). Really want this to work, don't want to warranty repair it (c/b sent back w NTF) & don't want to be without the phone for a couple of weeks. BUT, it's still under warranty - clock's ticking, though.
Fingers crossed