I'm unable to link between these 2 portals, despite no blockage or anything.
It looks like there's a blocking Link between the Portals you are attempting to Link.
There is a link blocking it, but because it goes so closely over the northern portal, it looks like it is part of it.
Checking intel, assuming that the link I have professionally "underlined" in red is anchored to the northern portal, the portal status should show 9 links in total, however, only 7 links are actually anchored at the portal. If you try fiddling around with intel, it sometimes glitches and shows a clear seperation.
These are the two anchors of the blocking link: