we need more inforamtion about your setup, this error produce internally ? if so how is your traffic flow going outside, in the path from user pc to internet, there is some kind proxy or thread analysis running to get this.
Ngrok site uses SSL and if you open the page with http it will be redirected to https. In your case some thing in between is blocking the page itself. Are you using Cisco umbrella..? Can you check nslookup from your PC whether it is resolving properly...?
I think for now we are only guessing how your network, based on that we are suggesting. either you have some filters which is part of the network. Since we do not able to reproduce the isse you were mentioned.
