PMS Remote Access keeps disconnecting after 15 minutes or so, how do I fix this?

I ran a port check for my port on my ISP and it isn't blocked. I am using the default port. I have disabled secure connections as I read in another post that may be causing the problem. No effect. I also have my server hardwired to my ISP router. So I think I ruled out the possibility of a double NAT. I just updated my server software to the latest version 1.1.2.2680
My system is a MAC MINI 2012, i7 Quad-Core 2.3GHz and 16 GB RAM running El Capitan 10.11.6