When typing in the command bclaims guild join the list of guild options does not appear. This is most likely because the guilds are read on initialize from the world file. When a player joins, they should have the server list sent to them.

I temporarily added a list command to see exactly what the problem was, and it doesn't seem to involve sending a server list. This error occurs in the console:
Could not serialize net.cflip.bineclaims.command.GuildArgumentType@561907a4 (class net.cflip.bineclaims.command.GuildArgumentType) - will not be sent to client!
So this seems to be the cause of the guild list not showing on the join command.