MC Version - 1.18.2

Mod Version - 2.0.1.2

Whenever a server is restarted, the wither storm will despawn unless a player manually loads the chunk that the wither storm was in before the server restart,.

If you teleport far enough away that the player will not load the chunks the wither storm is in, then restart the server, the wither storm will no longer chase the player or do anything until the chunk it was in is loaded again.