Altheran

So, I updated my BIOS and disabled any and all power management settings ... Rock solid for the last week.

Note that I did nothing past my "Here is where I might pratice caution with what it is suggesting :" comment in the middle of the instructions.

Edit : BIOS "only" finally didn't fix it for good (made last longer tho), I had to edit my /boot/config/go file and added these lines at the end (or in the order it makes most sense for you)

# Ensure NVIDIA driver is initialized & kept warm between clients

modprobe nvidia
/usr/bin/nvidia-smi -pm 1

# Optional warm-up query (fails fast if device absent)

/usr/bin/nvidia-smi -L || true

Well, I got it !

Updated to 7.0.0 beta4 as there was a few IPv6 fix listed for docker, didn't want to take chances.
Didn't work.
 
Then I removed the bridge as I don't really use it and also enabled host access to custom networks. (Edit: host access created a duplicate of my Unraid IP under a new MAC, triggering some annoying notifications in UniFi. I reverted back this setting to Disabled, and everything keeps working fine, so no need for host access for IPv6 to work, it was just the bridge ! )
 
Then the subnet appeared in my container settings !
 
Now to define the IPs, all I had to do is setting the Fixed IP field properly (adding the IPv6 following a coma after the IPv4.
 
Instead of : [ 192.168.1.2 ], do this : [ 192.168.1.2, 2606:6d00:zzzz:zzzz::1:2 ]
 
Thanks for pointing me in the right direction