"SpectreLib" missing on server side, but it's not installed clientside either

Trying to get the Better One Block modpack by egocrafte going on a brand new server. Every time I try to log onto the server, I get this:

Channel of mod "SpectreLib" failed to connect: This channel is missing on the server side, but required on the client!

But I'm extremely confused by this because SpectreLib is NOT a mod in this pack. In fact, there isn't even a version of it out for 1.21.x yet according to CurseForge. Would love some help in figuring out what it wants me to do here.

Also, the error I get on the server console is that the client version is incompatible, but I am running NeoForge 21.4.135 on both client and server.