Sometimes, the Wither boss's attacks deal no damage

Steps to Reproduce:

1. Summon a command block.

2. Set the command block to "Repeat" (purple) and set it to "Always Active." Then, enter the command: /effect @e clear.

3. Summon a Wither boss and an Iron Golem.

4. Observe their fight and pay attention to the Wither boss's attack damage.

Observed Result:

Sometimes, when the Wither shoots a Wither Skull at the Iron Golem, the Wither Skull does not deal any damage and does not harm the Iron Golem.

Expected Result:

The Wither Skull should deal damage every time it hits.