When a tipped arrow has an instant effect, for example healing or harming the effect is not applied to the shot mob or player.

How to reproduce

1. Prevent you from regenerating automatically, for example by using the following command:

   /gamerule naturalRegeneration false
   

2. Use the following command twice

   /summon Arrow ~ ~5 ~ {damage:0.5d,player:1b,Potion:"strong_healing"}
   

You will see that you only take 0.5 damage but don't get any health back