I discovered a strange, blank link in this user's Top Network Posts:
The above link and screenshot are of the user's Unix & Linux site profile, but this issue can be reproduced on any of the user's site profiles other than Meta Stack Exchange (as the blank post appears to be on this site, and posts from the same site are excluded).
The link seems to go to https://meta.stackexchange.com/questions/-2147482643/330386#330386, which features a really negative question ID (close to the lowest value that can be represented by a 32-bit signed integer, specifically
-(2^31) + 1005), and lacks the title in the URL that is present in all of the other links. It leads to a 404 error.
Going to the actual answer 330386 seems to go to an actual answer on a question migrated to this site, which happens to have a score of 13 (as of the time this was asked).
Why is the question ID incorrect here? Based on the duplicates, it seems that this affects posts (both questions and answers) that were migrated from other sites: somehow, the question ID seems to be getting messed up.
Update: It looks like the above linked user has deleted their account on this site, so the issue cannot be reproduced on the profile I originally reported. It can, however, be reproduced on this one. The errant link in that profile is https://ell.stackexchange.com/questions/-2147480236/184031#184031, and the errant question ID seems to also be close to the lowest possible 32-bit signed integer,
-(2^31) + 3412.