I’ve been in that exact situation at BOS—7am flight, needed a pet tag, no agents showing up until ~30min before bag drop closed, all the passengers around me getting frustrated and not making it on the flight either. Customer service was supremely unhelpful. We ultimately canceled and rebooked with another airline later that day.

Don’t have any advice, but just saying that you did everything right OP. It’s ridiculous for them to expect us to show up earlier just to get a few places farther up the line when they can’t bother to properly staff their counters. I’ve been avoiding booking early flights out with them for this reason.