Steps to reproduce:
Open a world
Go into
/gamemode creative
Fly into the air
Now, run
/gamemode spectator
Double tap space/space bar, depending on your platform
And finally, go back into
/gamemode creative
Notice how you fell to the ground?
When switching back to creative, the game is supposed to remember that you're still flying.
Potentially what's happening: the game thinks you're somehow turning on/off
flight by double tapping space/space bar in spectator, even though it's impossible to turn off flight in spectator, and you're still flying.
I can confirm. relates to MCPE-157059
It does not work the other way around (it does not turn on by pressing two spaces if it was turned off).