I am getting this error at startup (https://hastebin.com/otezowoxeh.css) on one of my servers and it seems like its an error with tab complete? But idk if there is a way to bypass this or if i just need to ignore it. It doesnt seems to do anything to tab completion.

Plugin Version: 4.4.1
Server version: CraftBukkit git-TacoSpigot-bf023c7d (MC: 1.8.8) (Implementing API version 1.8.8-R0.2-SNAPSHOT)

LuckPerms uses Brigardier which is a Mojang library for the 1.13+ command suggestion.
It normally wouldn't load on versions older than 1.13.
Try updating to the latest dev build of LP.

If it still causes errors, try changing the server to PaperMC

Thanks that fixed the issue!