Ahoy! Welcome to the forums. Your nautical post is reminiscent of when Tango our FreePBX frog mascot earned their sea legs sixteen years ago when one of the lead developers @plindheimer went with Tango Off to the Carribean for some R&R. 
Even with IPv6, that shouldn’t matter much for your LAN VoiP connections, unless the phones are trying to reach out to a remote provisioning server.
How many are connected ? Are you seeing any attempts by the phones to register with the PBX ?
Please filter and upload some logs to our pastebin.freepbx.org pastebin, and/or consider some screenshots.