If I am understanding you correctly, they removed all contingencies except the one regarding the HOA? If this is correct and they were to back out of the deal now, their refusal to go forth would technically need to be tied to the HOA.
Sounds as if the main problem here is lack of communication or a possible miscommunication. In any event, you and your agent might want to have conference call with escrow and the buyers' agent to find out exactly what's going on. If all else fails, you may want to contact your attorney to discuss your options.
Best of luck,
Finding a property or a buyer is a very small portion of the professional advice a Realtor provides.
Right now it sounds like there's a delay in closing and I don't blame you for getting nervous You issued a notice to perform which was the right thing to do. Hopefully, it will get resolved..if not, I advise you to consult with a real estate attorney.
Best of luck.
I hope this helps.
Did you choose the escrow company or did the buyer? If the buyer selected the company, I'd rely on an attorney. Your listing agent should also be able to assist you.