Pi-hole GUI admin performance

Hi all,

Maybe some of you experience slow GUI admin performance of pi-hole running in a docker as I did.
My setup is a synology NAS 218+ with running several containers using docker on the NAS.
As many of you, I think, I followed the step-by-step installation procedure kindly made available by others. In my case I used this one, How to Install Pi-Hole on Your Synology NAS – Marius Hosting
I ended up with a working setup, blocking ads and displaying sound statistics. The pc's, laptops, tablets and phones where perfectly directed through the DNS pi-hole without the annoying ads.

So far, so good.

However, the admin web interface of pi-hole itself was painfully slow. It took more than 30s to more than a minute to switch from the tab dashboard to settings or the whitelist menu.

It was not until I specified the ServerIPv6 address (of the synology NAS) in the environment variables of the docker environment of the pihole container, after that the GUI became way more responsive.

It turns out that may router (fritzbox 7360) also relies on IPv6 addressing and routing,

Maybe others experience the same problem and can try to add this setting.
Regards,
Ton