I have a similar issue with a mob farm I built, The farm levels will be 0 light, but when unloading an loading the chunks, there is a chance that random light will appear on the mob farm levels and I have to clear the cache of the world and run it again to have it reset to normal... This is very irritating
This issue can't be a duplicate and I don't see a fix on the other reported issues... This issue is that only phantom mobs are not spawning on the Server of 1.14. Yet they will spawn in a Single player world. Every other mob as well as the aggressive mobs do spawn on the Server.
This is the .JAR server file downloadable from the Mojang Website and there is no setting I can find to change this.
There where no block nor any sign or noise of any phantoms above my head, just the normal mobs... note that this is only on the 1.14 server, the normal single player has phantoms. and yes I was on the surface.. pillared up to avoid ground mobs, but still no phantoms... a bit worried if I can repair elytra if no phantoms on the server without mending books.
@Fergus Young, If you edit your world and optimize it with clearing the cache, Does it temporarily fix your lighting or does yours stay?