Can you long rest or short rest?
If that doesn't work, maybe try turning it to turn based mode, so you can "pass" your characters' turns, and try to force the prone to wear off?
I've never had this issue before. I have had Bulette "attack" then run off, but not to the point where all my characters were prone. Usually only 1 gets knocked prone.
Last edited by Lillith; 05/12/23 04:43 PM.