Background: when question is migrated from site A to site B and the author doesn't have account in site B, their name will appear "gray" until they log 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, their name will stay gray and unclickable even after they 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.