All potion types and area_effect_clouds that should apply potion effect levels 128 or greater apply them as level 0 effects.

Expected Outcome:  

All potion types and area_effect_clouds that should apply potion effect levels 128 or greater apply them as level 128 effects.

To Replicate:

Video:

1) Give player jump boost 128 through the following command. Notice how the player cannot jump; this is jump_boost 128's expected effect.

/effect give @p minecraft:jump_boost infinite 128 

2) Check effect Amplifier in player's ActiveEffects using the following command. It reads -128b, representing level 128 jump_boost. This is the expected outcome. 

/data get entity @p ActiveEffects 

3) Clear the current jump boost.

/effect clear @p

4) Give the player a potion of jump boost 128 through the following command.

/give @p potion{CustomPotionEffects:[{Id:8,Amplifier:-128b,Duration:-1}]} 1 

5) Drink the potion and try to jump. You will be able to jump. This is not the expected outcome.

6) Check effect Amplifier in player's ActiveEffects using the following. It should read -128b, representing level 128 jump_boost, but it instead reads 0.  

/data get entity @p ActiveEffects