High-level potion effects return to level 1 upon reentering a world

How to recreate
Use "/effect give @s minecraft:jump_boost 1000000 150 true" to give yourself Jump Boost 151.

Leave the world.

Reenter the world.

Use "/data get entity @s ActiveEffects" to view your current potion effects.

The jump boost effect (The one with "Id:8b") will have an amplifier of 0, not 150.