We have seen instances where the carrier’s proxy was stopping DynDNS updates after a reboot of the router.
Changing the port to something other than port 80 helped. DynDNS can use port 80 and 8245 for HTTP and 443 for HTTPS. See the following link for details: https://help.dyn.com/remote-access-api/perform-update/If you still have issues with DynDNS proxy there is another service which is free
https://www.dnsomatic.com/This can work against a number of different DDNS services as well as DynDNS
Feb 27, 2019