There are more ports used by the game. You can find the other ports mentioned in this document:
https://support.zwift.com/en_us/check-your-internet-connection-error-SJtFv63fr
More info about connection error messages, what they mean, what to do about it:
Occasionally rebooting the router helps as well.
I’m not sure where you are located but there was another report of connection problems in China recently.
https://forums.zwift.com/t/the-problem-of-network-connection-error/611532