These problems are either related to your bad configuration or poor careless design of the equipment you are using, can't really fault ipv6 for that.
@superczar weren't you using mikrotik? If yes, then there is likely a config issue in your setup. If you are using UI and seeing this, then I am not surprised.
Its not a configuration issue per se, I am using opnsense..
While I can assign each gateway its own weight and priority, you can't have cross stack prioritisation
Had both ISPs been dual stack (or had they both been v4) , then it would have been fine..
Similarly if i force ipv4 prioritization over ipv6 (which is pointless), it will still be fine
But this unusual scenario where the lower weight ISP is the one with a dual stack , and the other isn't ends up causing this..
This will remain true regardless of whichever soft router distro I or anyone use
If there is actually no firewall then the obfuscation of the internal network might help but at that point I would consider it insecure regardless.
No - thats just internet/reddit speak
NAT is not obfuscation.
Unless you explictly allow traffic from outside to come in on to a device on a NATed network, you
cannot have an out to in breach .
Since v6 = no NAT, the side effect is you can certainly have an out to in breach
As for in to out breaches, thats a different story altogether.. but i dont think that is what is being discussed here