Unable to forward port 443 on Pace 5268AC
I'm trying to setup a web server at home for fun and games. A normal HTTP server on port 80 works fine. However, I setup a redirect to HTTPS on port 443, but the gateway does not allow me to forward that port. It tells me:
The port 443 in the service conflicts with the device managed port 443.
When I enable "DMZ plus" or "IP passthrough" to the server, port 80 still works fine. In fact, it returns a redirect to port 443, but when the browser connects to port 443, it gets a broken TLS cert and an empty http body.
Port 443 is not one of ATT's "special ports" that they block, so there should be no reason this is failing.
I read online that factory-resetting the gateway can fix this, so I tried that. I reset the gateway, reconfigured my wireless network, re-enabled the "DMZ plus" thing to point to my server, and the HTTP/HTTPS redirect worked correctly!!! ...for about a day. When I checked the next day to work on the server, the same "redirect, broken cert, empty body" problem was happening. I know it's not my server, because when I change the DNS record to point directly to the local IP address instead of my public one, everything works great consistently.
I checked everywhere I could, and there seem to be no clear solutions. It is clearly a recurring problem though:
We have both fiber internet service and Uverse tv service, including a few wireless tv boxes. Here is the gateway information: