Reproduce:

• /execute in aether:aether run tp @s 0 100 0
• /give @s aether:golden_parachute
• jump off island
• use parachute
• wait 2s

branch 1.16 commit 367be79

I've seen no other reproduction of this issue so I doubt its an Aether issue.

Turns out this happens when falling too

• /effect give @s minecraft:health_boost 1000 255
• /effect give @s minecraft:regeneration 1000 255

And then before dying got "flying is not enabled"