Try to change the port number in settings and restart your desktop/laptop, it might work.
I am experiencing the same problem but on 9.6.10 and 9.6.11 versions of moddeler….
I tried – deleting moddeler, switching moddeler, deleting the project files, updating java and JDK, and fixing the port-number……. still stuck and this is blocking conversion proces…..
Once I connected to our companies VPN I was able to avoid this issue. I believe a web traffic monitoring application called Netskope, installed by our security team recently, attributed to the problem. In the past I had no problems with Studio Pro on or off the company VPN. Now it appears I must be connected. I hope this helps someone evaluate their own companies security apps when seeing this error.