@here, after a discussion with the tech crew we realized there are two separate issues.
One, that @austin.pray linked here, when knobs change their values without touching, has a pretty simple explanation and a way to fix it. The faulty encoders may be touching the metal chassis of the Play+.
All you have to do is to try to move them up and down and left/right to bend them a little (carefully 
). I had the same issue with my Play+ and it solved it perfectly. I don’t have to set my Knob Double Tap: Off anymore.
Unfortunately, the second one, posted by @asciimoo and @alxzndr, about flickering between the two states when a knob is held is still a mystery, and we are currently working on it.
I will post any updates here: Flickering touch-knobs in play+