Forge: 36.2.42
Version: v1.0.0

I installed UltimateSpawn and set my spawnpoint to be in faithfulbackrooms:level_0, yLowest to 52 and yHighest to 52 (the hight of the floor in the dimension). I spawn there normally upon logging in the first time, but then when I die, I firstly respawn in the overworld and the TPS stops for some time, and only then I get teleported to faithfulbackrooms:level_0 again.
P.S. My TPS is fairly low the rest of the time too.

I ran a spark profiler, it says that process dev.denismasterherobrine.ultimatespawn.utils.SpawnHandler.handleSpawn() takes up 85%, even more than it takes to tick the world itself. Here's the link: https://spark.lucko.me/ymzntbXH5k

If you need any additional information, feel free to ask.

Hello, thanks for the report. The link is unavailable right now for the investigation, however, this should now be not such a problem since 2.x.0 versions of the mod, when yLowest and yHighest are the same. Probably you need to specify yHighest to 53 or something, so there were any space for the player to be spawned.

Man, you're the goat! I have already lost hope, because the modpack I was working on at the time really depended on this one mod. Now it loads instantly! Gonna continue working on it!