Happy I found this, confirms I'm not crazy. Same deal, one of the Ultrastik 360's has a drift. I was able to narrow it down (I have like 10 inputs going on) using the Ultrastik 360 app.
I'll try the removing magnet technique. I've already had to replace one circuit board due to the usb connector coming apart (and something they should fix, support usb-c or something else).
UPDATE: I sort of got one of the 360's fixed by tightening the magnet down -- although there is so much you can do, the magnet is made to be loose or something. The player 2/Ultrastik 360 started doing the same drift too... and tightening down doesn't seem to work. I ended up just throwing it in a box and getting a standard 8-way joystick off amazon. I really wanted to get these joysticks to work, the flexibility of changing to 4-way etc was great, but seems like they have to figure out this drift/magnet issue first.