@DaveEdi
Hello Dave,
Basically, the Deco units will keep synchronizing with the NTP servers in your area to update the time setting on the network when you first set up the internet on it.
As per your description that your Deco M9 Plus do lots of lookups to the NTP server in seconds, it seems that they have a hard time to get a response from the NTP servers, can you please check if there is a limitation on your modem or network which blocked this lookup? If there are such settings, try to delete them and monitor the logs again, you may also change the DNS server on the Deco or on the gateway to a third-party one, such as google's 8.8.8.8 and 8.8.4.4 to check the results.
Hopefully, that answers your question but let us know if you need more details.