Hello! This is an issue we've tried to find.
We've noticed if people tab out, or simply move to another screen with their mouse when they come back it's gone.
Re-logging will fix this, but we're trying to figure out why it vanishes in the first place.
(Some reports also mention that they went into camera mode to take a screen shot and the mouse also vanished)
Thank you for reporting! I'll add a tally mark to the list for this issue occurring.