Update:
After a full factory reset and restore from an iCloud backup that predates this issue by a few weeks, I spent a more than 24 hours using my phone normally, browsing normally, but not visiting this site. I experienced no redirects or popups at all.
After more than 24 hours, I decided to visit this forum as a test. Remember, this forum was the only site I experienced this redirect problem with.
About 2 minutes after I visited this site again, I got the same redirect to goodluckdog dot space. Again, only on this website. Not others.
So I downloaded Taptalk and I’m hitting the forum via the app on my iPhone. So far so good. Not seeing that redirect at all as long as I avoid hitting this forum via Safari browser on iPhone.
YMMV, obviously