I did some more testing since I had it as well. It’s not that much of an issue since it affects only individual users, not the whole user base.
In short, an example link:
What is on (secret) sale? - (2nd new thread) page-20
Once you visit that one, something happens and your IP gets banned (or whatever weird dark magic happens in the background). You get Access Denied for like 10 minutes, after that you can access the forum again.
The Access Denied seems to be IP based, I tried with different browsers (firefox, chrome, edge) on my PC. All on the same PC had the same Access Denied issue, even ones where I wasn’t logged in. So it’s not a cookie or browser thing. When I tried on my Phone which was going over the same WIFI the same issue occurred. When I disabled WIFI on the Phone and used paid data tariff the forum worked as usual.