Hi !
I am having the same issue, or a very very similar one.
I installed ubuntu server and followed instructions here: https://docs.cloudron.io/installation/
But I am stuck at this step :
Once installation is complete, navigate to https://<IP> in your browser and accept the self-signed certificate.
It get stuck at loading until I get a "connection has timed out" error
Installation went OK and I can open the setup page using the local ip, so I guess the issue is with my ISP router
I am in France and the provider is "Orange"
I associated a fixed local IP to my server mac address in the livebox settings under DHCP/DNS .
And I also created rules to forward ports 80 and 443 under NAT/PAT but then I removed those in case it was messing with UPnP (wich is enabled by the way).
None of that worked 
Can you help me ?
P.S. I registered an account on the chat since the OP question was resolved there but I do not have access to it yet