(I'm coming here from Meta Stack Exchange. I'm here because one of your users attempted to ask about one of their problems over on that site, where it was first marked off-topic as a site-specific issue, but they're unable to post here due to an issue with their account which I'm about to explain.)
This user has an account both here and on Meta Stack Exchange, and has a per-site meta profile. Yet when one of their Meta Stack Exchange posts was migrated to this per-site meta, the question wasn't properly associated to their meta profile here; instead, their username just showed up as grayed-out text. This is to be expected when a question is migrated to a site where the author doesn't have an account, but the author does have an account here. This means that they can't participate in that question.
Also, strangely, their meta profile doesn't list their "other communities"; it instead mistakenly says that they are not participating in any other communities (while their main site profile does list their other communities). This is incorrect; per-site meta profiles should list other communities (see my meta profile here for instance).
The user claims to be getting a server error when attempting to access this per-site meta. Upon further investigation, we realized that this seems to happen on attempting to log in, and otherwise they appear to be logged out.
Given that I've had a similar issue with one of my chat profiles, where something was wrong with its account association and I was getting a server error whenever attempting to log in or use the site, I think that the central issue is that their per-site meta profile isn't properly associated to their network account, so whenever they try to login it tries to create a new profile, but fails because an existing profile is already attached to their site (not network) profile. That's also why the migration didn't associate properly with their existing profile, since it's not linked to the network account.
Can a moderator please ask an employee to resolve this issue? We'd like the user to be able to use this site without trouble, so they aren't forced to ask on Meta.SE where their questions about this site will be marked off-topic, and migrations won't help because they can't participate in, or even see, their questions.