Not replying to anybody in particular, just wanted to post this in case it helps somebody out in the future.
I was getting a 502 Bad Gateway error with SWAG for a couple of days and it was driving me nuts, every solution I looked for came up with "Did you enable Host access to custom networks?", but what had actually happened is my resolver.conf (at appdata/swag/nginx) had gotten stuck with some random IP address.
Simple delete of resolver.conf and restart of the SWAG container and everything was running smoothly.