The bug

When a player/mob gets hit by an arrow with the damage:0.0d tag, the arrow doesn't apply its CustomPotionEffects to that player/mob.

Steps to reproduce

1. Summon an arrow with a damage of 0.0d above an entity/player

   /summon minecraft:arrow ~ ~2.3 ~ {damage:0.0d,CustomPotionEffects:[{Id:20,Amplifier:0,Duration:20}]}

   → The arrow won't apply the minecraft:wither level 1 effect for 20 ticks.

2. Summon an arrow with a damage of 1.0d above the entity/player

   /summon minecraft:arrow ~ ~2.3 ~ {damage:1.0d,CustomPotionEffects:[{Id:20,Amplifier:0,Duration:20}]}

   → The arrow will apply the minecraft:wither level 1 effect for 20 ticks.

Code analysis

EntityTippedArrow.arrowHit(entitylivingbase) is called from EntityArrow.onHit(raytraceresult) only if the entity is attacked.