Do you have any additional firewalling features enabled on the router or camera? Connectivity depends on a P2P connection being established via a 3rd party provider called ThroughTek / TUTK. If you have such firewalling features turned on, disable them. They are rarely of any use.
After researching I now believe the issue is with the ASUS router. I am on Merlín firmware. They recommend disabling the “airtime Fairness” feature to play nicely with Wyze cameras, but the Merlin firmware does not have this feature. I am considering reverting to factory firmware for this ASUS router now.