What happens

Starting with 1.17.40, I started seeing "Your game is being saved, please do not turn off your device." 

More info

Sometimes (maybe 20% of the time) the message never goes away (have waited over night a few times).

If I end Minecraft before the message goes away, then the results are random (sometimes things seem ok, sometimes I'm back in time from before I saved).

Since the message sometimes never goes away and the game doesn't fully save, this is basically data loss.

Haven't seen this message before in the year or so playing on this machine.