I just wanted to post this, in case it saves anybody the headaches that I've encountered. My ISP (Webpass) uses carrier grade NAT for IPv4, and native IPv6. Since port forwarding from my router does nothing for IPv4 when carrier NAT is being used, I thought it was best to enable IPv6 support on the Plex Media Server via "Settings > Server > Network > Enable server support for IPv6".
This allowed me to connect via web browser by IPv6 address to my server directly, however would not allow me to use any of the Android apps, etc. As well, whenever I attempted an indirect, Plex Relay, connection it would fail and on the server it would immediately output the following in the logs:
[PlexRelay] connect_to localhost port 32401: failed.
Every time I retried, the same message would appear in the logs.
The only way that I was able to get Plex Relay, and therefore my Android app, etc to access my Plex Media Server from outside my network was to actually disable IPv6 in the end, which allowed Plex Relay to work properly so I could connect indirectly.
Does anybody know, is there indication on when IPv6 support will be coming to the clients?