Hello,
I'm new and I'm reviving this one year old topic because I'm facing the same issue. I bought this AP and shortly after I noticed that I was loosing IPv6 connectivity after a couple of hours/days of usage. I've been in contact with D-Link french support since end of August around this issue, tried proposed firmware (latest being 1.30rc055) with no luck.
They asked for a set of network dumps to get better view of the issue, I also took the liberty to do some closer monitoring of the failure and tonight I finally noticed something. I configured my router's radvd to issue IPv6 RA quite often, and on my laptop I checked and logged the IPv6 addresses every 30 seconds.
This exposes the IPv6 prefixes lifetimes:
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As you can see, we clearly see a regular update until at some point nothing happens and ultimately we run out of lifetime without any new RAs reaching.
Now, what is interesting is that the first time we do not get a RA to update the lifetime correlates in the syslog of the AP with a bunch of messages:
Jan 5 05:45:30 ap [Wireless]Deauth:STA C8:D3:A3:xx:xx:xx(reason 7)
Jan 5 05:45:31 ap last message repeated 9 times
We get a Deauth reason 7, as documented in this topic. And the target MAC address is the one of the AP's Wi-Fi interface!
Of course, I've shared this with D-Link in my ticket and I'm now waiting for a reply from their developpers.