Eversince the 1.21.5 update, we noticed that the nether has become very, very dark (pitch black, not deep red as it usually is), even from short distances. Initially we asssumed this was from Vanilla Minecraft itself, but after entering a vanilla game mode, we confirmed that the nether isn't supposed to be this dark. Turning up the Brightness in Video settings does not fix this. Players have been having trouble navigating through the nether, so we're hoping there's a fix for this. When testing this in vanilla Minecraft, the "darkness" is nowhere near this pitch black. Screenshots attached as below :

Disclaimer : These screenshots do infact come from two different players on two different systems. We also do not have any additional resource packs/shader plugins installed on the server. The only plugins enabled during this are EssentialsX, GriefPrevention and LuckPerms.

EXHIBIT A, the Minecraft server running with Spigot: 
As you may notice, the darkness/lighting is just very, VERY dark even when near lava.

{+}EXHIBIT B (Vanilla Minecraft)
{+}As you can see the draw distance is much more visible in vanilla, and the distance is in deep red as opposed to pitch black from Exhibit A.

This does not cause a crash, but it does effect gameplay visibility in the nether, and considering its already dark in there; we hope there's a fix for this.