The bug:
I teleported myself up and my "OnGround" tag was set to 1b for one tick.

How I recognized the bug:
First of all I added a scoreboard objective with the command

/scoreboard objectives add store dummy

(screenshot 1). Then I placed a repeating command block that was set to always active with the command

/execute as @a[nbt={OnGround:1b}] store result score @s store run data get entity @s Pos[1]

(screenshot 2). Next I flew in creative mode somewhere in the air and used the command

/tp @s ~ ~100 ~

(screenshot 3) to teleport me 100 blocks higher. As I set the objective store in the sidebar my y-coordinates were written there(screenshot 4). After one tick the OnGround tag did change back to 0b and the y-coordinates in the sidebar didn'
t update anymore.

I repeated the test with an armorstand and also his y-coordinates were written in the sidebar(screenshot 5).

So I think this is a bug and I hope that it gets fixed soon.