Probably a JavaScript error at the time you checked..?
I still work a lot on these pages, so they break from time to time while I'm experimenting with new features.
Check again, I just went there and I'm not seeing any problems... (With Firefox at least.)

Premium tags have always been in the /tags/ page, not the /matches/ page, if that's what you meant..?

Not when we press the library section? That would be a good place, because the only other tool I know online takes forever to load. I have so many games that it is difficult to search by tags some to try.

No, I never wrote a tag filter. I only wrote a multi-tag search, remember? That's the premium thing... ;)
Tag filters are vanilla on Barter so they wouldn't be premium here. (Not like I'm planning to have a lot of premium filters either.)
I may do multi-tag filters on lists though in addition to solo tags, multi-tags would be a good contender for premium, just like on /tags/.
I will eventually implement filters on lists, of course. Just... Give me some time :) I need to finish multi-edit for now, as well as try & implement export to Barter, and bundle & wishlist import from ITAD.