@Riley_S 

Thanks for the reply!  I tried the 1.1.1.1 DNS and still no improvement.  I changed the ethernet port used for the WAN connection and no improvement.

The issue is for all devices using the Deco wifi, though no parental controls or sites on the block list.  Slowed connection is resolved when hard wired into the ISP modem with ethernet cable or when using Tor.

Traceroute typically looks like this (links modified to [dotcom] to conform to posting rules):

  1 5 ms 6 ms 4 ms  192.168.68.1

  2 16 ms 15 ms 14 ms  142-254-184-029spectrum[dotcom] [142.254.184.29]

  3 29 ms 31 ms 30 ms  lag-62sndhcahr01hcharter[dotcom] [76.167.17.137]

  4 *    *    * Request timed out.

  5 *    *    * Request timed out.

  6 *    *    * Request timed out.

  7 *    *    * Request timed out.

  8 *    *    * Request timed out.

  9 *    *    * Request timed out.

 10 *    *    * Request timed out.

 11 *    *    * Request timed out.

 12 *    *    * Request timed out.

 13 *    *    * Request timed out.

 14 *    *    * Request timed out.

 15 *    *    * Request timed out.

 16 *    *    * Request timed out.

 17 *    *    * Request timed out.

 18 *    *    * Request timed out.

 19 *    *    * Request timed out.

 20 *    *    * Request timed out.

 21 *    *    * Request timed out.

 22 *    *    * Request timed out.

 23 *    *    * Request timed out.

 24 *    *    * Request timed out.

 25 *    *    * Request timed out.

 26 *    *    * Request timed out.

 27 *    *    * Request timed out.

 28 *    *    * Request timed out.

 29 *    *    * Request timed out.

 30 *    *    * Request timed out.

Trace complete.

Traceroute does not time out when hard wired to ISP modem.

Thank you for clarifying the MAC cloning procedure.  I tried cloned the MAC address of an old modem and that too resulted in the router losing internet connection entirely after rebooting.

The problem is still persisting: Facebook/Instagram/WhatsApp are not usable when accessing them through any device on our wifi.  No other services are impacted and the problem is not present on other networks or on a wired connection to our internet.  Any other suggestions?