Any overflowing levitation effect on players (Higher than amplifier 127) forces the OnGround tag of the player to 0b for a few seconds after the effect has worn out. This might also be the reason why the jump statistic breaks during this period as well. Here is how to reproduce it:

Run the following command:
/effect @p minecraft:levitation 5 128 (128 can be higher, too)
Shortly after landing, run this:
/testfor @a[r=0]

The expected behaviour is for the command to return your username. However this isn't the case.