The final prayer of the spell Prisa says:
When the spell ends, the target. can not move or take Actions until after his next turn, while a wave of lethargy sweeps him. (PBH p 250)
If a creature like a wyvern, pegasus, griffon, etc. it is flying while hurried on (ie, under the effect of the Haste spell), does it fall when the spell Haste ends because at that moment the affected creature "can not move"?
A superficial reading of the paragraph under Movement of flight in the PHB seems to suggest that it would fall:
If a flying creature is knocked down, its speed is reduced to 0, or if not Deprived of the ability to move, the creature falls, unless you have the ability to float or it is held high by magic, as by the spell of the fly. (PHB page 191)
But I'm not sure that he has not lost some subtle nuances in the writing of the rules that would argue otherwise.
The Compendium of wise advice 2019 has this paragraph:
Can a flying creature without the floating feature stay in one place while it is in the air, or does it need to move each round? A steering wheel that lacks the floating feature. can Hold high without moving each round.
The language in the description of the spell of Prisa does not impose any formal condition (as Disabled, Stunnedor Restrained), nor does it say that the creature speed It is reduced to 0 feet. So I wonder if the words "can not move" in this context are enough to establish that a creature in flight must begin to fall immediately (as a wave of lethargy sweeps over it) or if there are reasonable grounds to argue that according to RAW or RAI it can remain high without "moving".