Contacted by a nice recruiter, had 3 rounds, including full onsite interview and hour long group presentation. I followed-up with thank-yous and a request for feedback. They never responded. When a candidate spends 3 rounds with you, and a day preparing a group presentation it seems reasonable to spend a few minutes telling them what did and did not work. Instead they did not respond via phone or email. This is the only company I have ever seen that totally ghosted after interviews. Very unprofessional.