I suspect Web Support would not know much if anything about this kind of issue.

The one time I had a problem with online check in, issue was a ticketing one: reservation had been changed but the agent had not done the necessary changes to associate the ticket (maybe reissue?) with the reservation.

In the end I phone the concierge who solved the thing for me. (I believe either it was a business class ticket, or I had a confirmed upgrade that had been preserved over the ticket changes.)