To me a few days of non-communication is completely unacceptable and is a huge red flag, especially if this guy (you said he) is on here actively posting which is basically just a huge "FU."
In my opinion, there are 2 routes to take on this -
1. be assertive and give him some sort of ultimatum. don't trash the guy publicly but let him know you will be writing an honest review of his work on X review site and will not be working with him in the future, or recommending him. let him know the only way to prevent this from happening is to respond with a plan of action and to follow up on that plan.
2. cut your losses and find a new developer.
I learned a long time ago if you want to be respected in business you cannot always make friends and you can't worry about making people happy. Sometimes this means sending people ultimatums, especially when you money, time and dreams are on the line. There is a lot of talk about depression and anxiety, which are very real things however these are not your problems. Good luck!