@SoCalWi-Fi 

If all Deco units are affected the issue may not be the Deco at all.  It could have to do with configuration or even something on the ONT or built-in modem.  A few things to try:

1.  swap one of the other Decos in to be the main unit.  Test the connection and see if the issue presist.

2.  Check the ethernet cable between the ONT and the Main Deco, swap if possible.  As the Ethernet ports are 10/100/1000 a Cat5e or Cat6 cable will suffice, no need to go to expensive Cat7 unless you have extra available.  

3.  Contact your ISP and have a line stablity test ran. 

Now if step 1 is successfull and the connection remains stable you may have a defective unit at which point you would need to contact the HD to request a replacement.