I've been having an odd problem with my QC20 in-ear headphones. Often (maybe 50% of the time?) when I plug them in to my Android phone, the volume/mic will freak out. The volume will go up to 100% or go down to 0% (the phone UI shows the volume control if I was pressing the buttons on the phone or on the cord), and the Android assistant will pop up (as if I was talking into the mic). I'll generally unplug and then re-plug until the problem doesn't happen. Sometimes I have to unplug and re-plug 5 or 6 times. If I can get over the first 5 seconds or so, and everything is fine, the headphones work fine for hours and hours after that point.
I thought some of the physical buttons on the cord might be "stuck", but playing with them doesn't seem to help or hurt (and none are obviously stuck).
I thought it might have been my old phone (a Samsung S5), but I recently upgraded to a Pixel 3 and the problem happens just as much. (The Pixel 3 requires a USB-C adapter jack, too.)
This happens if the headphones are recently charged or not.