The effect regeneration with infinite duration won't follow the amplifer, it regeneration your health similarly to, It could be that the game gives you the effect repeatedly as intended to infinite duration, that's why it fails to follow the amplifier.
How to replicate:
give yourself an regeneration on command, the amplifer must be 0. (/effect @s regeneration infinite 0)
now that you have the effect, try to damage yourself or you can just use damage command (/damage @s 19)
as you damage yourself, you regenerate your health quickly, this shouldn't happen because you have the amplifer of 0 (which is regeneration 1 from potion)
Expected result: it must regenerate your health slowly like how you regenerate with regeneration 1 potion works despite the duration
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