Why is link not possible over short distance with no apparent link in the way?

Firstly, here's the area I'm working in. Here's a diagram created from the map:
For reference, these are the locations in the diagram: (apologies that it's not in English, that can't be helped)
- A: 강의기원
- B: Brilliant Metal
- C: 대석길 안전음식 먹거리
- 1: 연향상가 패션거리
- 2: 교감
- 3: 기록탑
- 4: 반석수
- 5: 창조
- 6: 책을 펴자
The outer triangle was an existing one that I didn't create. I took some time planning how to best build links within and eventually settled on the plan in the diagram. I was about 50% successful. I was unable to make some links, but I don't really know why.
My plan was to travel down the numeric spine of the portals to collect keys, go to C first, connect each, then go to B and finish the connections, then travel back up the spine from 6 to 1 connecting each numeric portal. This is based on a similar process as described in this question.
When I arrived at B, I was able to connect each portal until I got to 6, which refused to connect (This is the black line in the image). There is no apparent link in the way. I tried upgrading the resonators and adding a Link Amplifier, but neither worked.
I had a very similar problem when I arrived at B. This time I started connecting from the bottom going up. I was able to connect to 6 fine, but when I arrived at 1 (red line), it refused to connect with very similar issues. I tried the same things, but had no results.
Eventually I walked back up the numbered portals, tried to connect 6 to C from 6, but it still failed (though once the "Link Possible" voice clip played, no actual potential link appeared when I tried). I traveled all the way up to 1, with no links possible between numbered portals (grey line), and was still unable to connect 1 to B.
In each case described, I had portal keys available. I don't see any links blocking the path, and distance shouldn't be an issue. I did notice that it was the last portal that I tried to connect (from B and C) that failed to connect.
What caused these links to not be possible?
Best Answer
I can't see clearly all the links, but I suspect that each of the points had 8 originating links on it (i.e. links going elsewhere) and this is the reason.
There's a hard limit on the number of outgoing links as 8, and maximum total of 12.
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