@Hiro27 

TP-Link support did a remote session on my system awhile back to look at the IPv6 issue.  After a few days, it seemed to start working, so that's the conclusion we came to;  that it was the MAC address being bound, and eventually it reset itself.  But later, it stopped working again, so I think there may be multiple issues.  Sometimes I can get an IPv6 if I keep releasing and renewing, but 99% of the time it doesn't work.  For now, I've given up trying to get IPv6 working with the TP-Link.

For what it's worth, I did some wire-sharking, with the help of another person, a few years ago to look at the IPv6 behavior when I was using Tomato firmware, due to the strangeness of it.  What we found was that PLDT doesn't respond to Router Solicitation messages.  But they were sending out Router Advertisements, on a set 20 minute interval (the timing should be randomized, but it wasn't).  So IPv6 connectivity is dependent on receiving the RA every 20 minutes.  If it's missed for some reason, you won't have connectivity until it's received again.

So with Tomato firmware, after a router reboot or a release/renew, it would take up to 20 minutes for IPv6 to start working.  Sometimes it would start right away, and sometimes there was a delay, depending on when the RA was sent out by PLDT.

My guess is that, when the RA is received right away, IPv6 works on the TP-Link.  If there's a delay, though, IPv6 is never functional, even if you let it sit overnight.

I've got IPv6 working now with a Mikrotik router, so I'll share a few things I found, in case it might help.

When the dhcpv6 solicit is sent, there are 2 servers I'm seeing respond, alternately.  One sometimes responds with "NoPrefixAvail" and the other "UnspecFail".  I'm not sure why this happens.  I'm speculating that it's a timing or binding issue, or a previous prefix that wasn't released and hasn't timed out.  The mikrotik will persist, though, as long as it takes, and it will eventually get a prefix.  It could be right away, or it could take an hour, or a day.  Once it gets the prefix, it seems to be pretty good at holding onto it, and even if you release it, it will usually get another quickly.

An important setting to get it to work consistently is to "Add Default Route."  Without it, it will sometimes work, but mostly not.  But with it, it almost always works.

Of course with the TP-Link there aren't many settings to change, but if that option were available, maybe it would help.