@kyosya. A Onewheel moving on its own sounds to me like a problem with the grip tape over the sensor. Search YouTube for videos on replacing your grip tape -- or get a new footpad.
Get an app to check your battery cell voltages for balance -- I use the Onewheel Community Edition app, but there are others. (Note: the XR only has 15 cells, while the Plus and V1 have 16, so for the XR one cell of the 16 in the app will read weirdly.) A solution I have read but not really tried for rebalancing the battery cells to get a more accurate percentage reading is to drain your battery to 'Captain Morgan' low battery pushback, turn the Onewheel off and wait a moment, drain it some more and again until it will no longer turn on, then charge it for 24-72 hours -- and hopefully that will correct the issue.