Basically, when you jump in place with jump boost 255, the OnGround tag acts a little weird. I know there are some unusual behaviors with high levels of potion effects, but this one seems more buggy.
The commands in the command blocks are:
scoreboard players set @a[nbt={OnGround:0b}] OnGround 0
scoreboard players set @a[nbt={OnGround:1b}] OnGround 1
Thank you for your report!
We're actually already tracking this issue in MC-10755, so I resolved and linked this ticket as a duplicate.
However, that ticket has already been resolved. Depending on the resolution, that can mean that it either will be fixed in the next version, or that it is not considered a bug and won't be fixed.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.