XF 2.2 403 on one single page of my whole forum


For some reason there is one single page in my whole forum that won't show and gives a 403 error:

I can get to the 2nd page at:

And from there all other pages, except the 1st page.

Or I can even go to the most recent thread in the forum at:

Every other single forum and thread throughout the forum works just fine, as far as I can tell.

So, any ideas on how to fix this?

If not, any ideas on how to maybe move those posts to another forum? I figure I could make another one and it'll probably work and I can just move all the posts.

Thanks for your help!