In the old days LinkedIn would tell you how someone is linked to you. That information is useful when you are trying to connect to a 2+ degree user and want an intro from your mutual contact.
Unfortunately, I can't find that information anymore. (As of 20200830) Is there a solution to this problem? From what I have googled, the answer is yes. What is the solution? Money -- that feature is now a paid feature.
From a Pulse post via LinkedIn on the hidding 2nd degree connections:
A few weeks ago LinkedIn changed their design. Things changed. Some good... some not that great. There's a few, but one of them that strikes me most is the fact that about 60% of your second degree connections are "hidden" in the free version of LinkedIn.