Somewhat related to this: Mouse pointer moving by itself - but there is no "keyboard mouse".
Currently my workstation, with a fresh install of Ubuntu 22.04 (and all updates) is experiencing phantom mouse movement. This did not happen on 20.04 two weeks ago. A few days ago, the mouse was connected, it was moving the pointer to the top-left corner, and clicking (bringing up the Cinnamon menu).
Today, with no mouse connected, the cursor is moving in a lazy lissajous within a terminal window, occasionally double-clicking. Desktop is set to "focus follows mouse"; sometimes I see the window loose focus for an absolute split-second, cursor warping about 1000 pixels to the right (to some empty desktop) before returning.
There was a mouse connected through a USB hub (along with the keyboard), but I have pulled the whole lot to switch it between computers. It's been disconnected for some hours.
Is this indicative of a hardware fault? It's really creeping me out. PC hardware is self-assembled: MSI-mothebroard, Intel i9, 64G RAM, maybe 6 months old.