Can wearing a tight bounty after hair PRP and microneedling may cause severe hair loss?

In  my opinion, unless there was a significant amount of swelling and your Bounty contributed to this situation, there should be no effect on the success of the procedure. Swelling could put pressure on the follicles which may decrease effectiveness. In a very small number of people undergoing PRP, there is an initial hair loss prior to the benefits.PRP hair md.com

It is unlikely anything you did would have caused the hair loss that quickly.  Wait a while and you should see continued improvement from your treatments.  It can take up to a year to see results from consecutive treatments.

Sometimes mild inflammation and swelling on the scalp after PRP can cause initial hair loss.  That's why tight hat or hair band are not recommended after the procedure.  I believe this is temporary and hair loss will improve in a couple of weeks.  Otherwise please consult your physician.