net-proxy/squid is using group id 31 for the "squid" group. This collides with the "guest" group in the standard /etc/group file installed by baselayout for FreeBSD. If a fixed group id is needed, then this conflict should be resolved. If not, enewgroup should assign the id dynamically. (net-proxy/squidguard and net-proxy/ufdbguard don't have any BSD keywords, but IIUC the intention is that they use the same group as net-proxy/squid. Therefore CCing their maintainers.)
Should be fixed in the tree. < enewgroup squid 31 < enewuser squid 31 -1 /var/cache/squid squid --- > enewgroup squid > enewuser squid -1 -1 /var/cache/squid squid etc.