Hey, I'm making a 1.16.5 modpack for some friends and myself, and tried to add your mod to the pack. It works completely fine on single player, but trying to add it to the server causes a crash on startup. I've removed all of the other mods in the pack, so the only mod that is loading should be BannerUnlimited, but it still crashes. I tested running it only on the client side and not the server, but it only caused desyncs between the two and didn't actually work.

Is there some sort of issue preventing this mod from working on the server?

If it helps, here's the server crash log from the last time I tried to load the modpack (this was after I added the other mods back in, but it was still crashing without them too):
https://pastebin.com/2LbvpXDh