[Phanx]

You're never actually registering for the GUILD_ROSTER_UPDATE event. Change:

for _, event in next, {
	"PLAYER_ENTERING_WORLD",
	"PLAYER_LOGIN",
} do
	management:RegisterEvent(event)
end

to:

management:RegisterEvent("PLAYER_LOGIN")

and add:

	if event == "PLAYER_LOGIN" then
		Calendar_LoadUI()
		GuildFrame_LoadUI()
		self:RegisterEvent("GUILD_ROSTER_UPDATE")
	end