Background: when question is migrated from site A to site B and the author doesn't have account in site B, he will appear "gray" until he logs in to site B and associate the accounts, then the avatar show and all is good. No problems here, same for answers and their authors.

Problem: if user from site A posted comments while the question was still in site A, his name will stay gray and unclickable even after he logs in and have account in site B:

This is the above question, but most likely it's global problem, not specific to that one occurrence.