There seems to be two different things going on in this thread.
First is the UI coming up and the second is the warning produced by the Python Cryptography module. I believe they aren't related as the warning is no fatal and the module continues.
So, for the UI, the following commands might help to troubleshoot what is going on:
iptables -nL INPUT | grep :443
ss -ntlp | grep :443
Those should show if the AS0_ACCEPT has been added to the INPUT chain in iptables. It should also show if openvpn-openssl process is running and listening on port 443.
If both of those commands produce expected results then it is installing the iptables rule and actively listening on the port. I think the next most likely cause of the problem is something with zope.
It should be noted that 2.9.6 is no longer the latest version of OpenVPN AS and you might want to try 2.10.0.
As to the warning from the Python Cryptography module, it looks like there is an issue with forking the already initialized random number generator when using OpenSSL version 1.0.2k that is bundled with CentOS 7. Looking at the python code making up the Cryptography module, it looks like if OpenSSL is version 1.1.1d or higher then the warning will no longer apply. The EPEL (Extra Packages for Enterprise Linux) for CentOS 7 has OpenSSL version 1.1.1k which would fix the potential issue which is causing the warning. It is just a matter of if OpenVPN AS is willing to support EPEL's OpenSSL for CentOS 7.
