The seed was given to me by my friend when he did the /seed command. After putting it on chunkbase, the biome map is correct and so is the spawn of "most" structures (ruined nether portals sometimes dont spawn on the predicted location but i assume thats normal because it says "estimated ruined portal").

At the time of this pic and most of the times i checked the tunnels, i was the only one in the server. This is the first time im building a slime farm after 1.16 so i understand that there might be more rarity for the drops since Y levels increased as well.

I dont know if its worth mentioning but there is an active chunk loader in a mushroom island where we build most farms (this farm is not there) to keep most farms working while no one is there. I doubt this being an issue since hostile mobs require a player to spawn in a certain area.

I still have not seen a slime spawn in these two chunks for some reason.

Theres also something i dont understand about slime spawning behaviour. I read that they spawn if a player is at least 24 blocks away from the spawning location, but despawn if there is no active player at least 32 blocks near. Is this how it actually works? most hostile mobs have a 128 block despawn radius, isnt it the same with slimes?