Multiple portals won't work properly

I'm playing around with making an Eternity map with portals. The first portal I made, after some tinkering, worked perfectly. But once I put another portal on the map, the player can only see through to the other side of the portal. Any attempts to cross just end up in the dummy sector behind the linedef. What is it I'm missing?

Are any linked portal errors appearing in the console? There might be a mismatch between your portals' physical positions.

If not that, try flipping the linedefs?

Yeah, there is one. The error I'm getting reads:

P_BuildLinkTable: sector 56 in group 1 contains inconsistent reference to group 0.
Linked portals are disabled.

What's strange is I don't see anything about how any of the portals are set up to signify something is wrong. The heights, physical sizes, and everything else is how it should be. The lighting level is different in the dummy sectors as well. I have four attempts at portals on the map. If I set the linedefs and tags to all but the first one I made to zero, then it'll work, as well as a plane portal I made. The other two wall portals have similar error messages.

EDIT: Discovered the issue. The sector connecting two different portals was shared, which somehow messed it up. The portals look strange now though, if you stand too far away they become a hall of mirrors effect.