I've noticed an odd ipv6 issue when connecting wirelessly.

ipv4 comes up straight away however ipv6 lags by about a minute sometimes slightly more.

I've reset all the networking, updated the drivers rebooted the wireless access points removed third party firewalls and vpn and the issue remains. Same with encrypted dns enabled or disabled at the pc or on the router.

The issue isn't present on a cable connection.

All the drivers are up to date and all the lastest windows updates installed. 

Any ideas?

Not actively/knowlingly using ipv6 but wondering if it could be a DNS issue of some kind?

Well for several minutes it gets a link local ip address dns ipv6 fails if you use DNSSEC it says falling back to standard dns. After a few minutes the ipv6 address comes up as does the dns.
Interestingly if you do a test for dnssec later it says it's not available for ipv6 just ipv4. So i turned it off. Not made any difference still slow.

The lack of any errors in any logs doesn't help either. I should try hot spotting from my phone and see what that does.
 

Just tried a different wireless card and the same thing happens.

Okay so a quick update. Definteley an issue with the 1060c.
Tried my old synology router as an wireless ap connected to the 3910 and ipv6 up straight away.
So what the hell are the 1060 doing. 

I started to type a few suggestions earlier but seemed to have closed my browser at some point; no matter - your latest has skipped a few things I was going to suggest.

Depending on your appetite for risk, have you considered doing a hards reset of your 1060, or even flashing a clean version of the firmware (you could try loading a saved config back in but there's probably some value in manually configuring again unless you have a profile you could deploy); I'd not blame you for not wanting to do that tho!
Would wireguard show anything useful?  It may show you the timings of the traffic between the devices?
Have you tried turning ipv4 off on the client (if possible)?  I wonder if there's a resource contention that means there's a queue that ipv6 is 2nd in line for?
You've got multiple 1060's?  Are they in a mesh?  Is it the same from all devices?  And if you have a mesh, tried different physical devices as the root?

I'm really just clutching at straws here - not something I've any experience of but might put a seed in your mind of things to try.