@TP-Link ,

Thanks for the quick reply. 

The diagram you provided is correct. At the moment, after encountering the issue, the secondary is wireless back to the primary.

It worked fine for a bit over a week after switching ISPs. I didn't make any changes to the wiring or to any other hardware not have I change any settings on the Helix or the Decos. 

I have not tried switching the secondary deco to primary. I can but I have ~20 home automation devices connected and I'm trying to avoid having to reconnect each one. Is there a way to switch the primary/secondary easily without redoing the configuration? 

I'm looking at adding another 1 or 2 units to expand my range once this is resolved. 

@TP-Link, 

The units were initially configured in AP mode and have never been put back to router mode. 

I tried switching Unit 2 to master as suggested. When I did that, I left the previous master (Unit 1) plugged in to the modem/router/switch unit and then plugged Unit 2 (the new master) into the modem/router/switch. The result was the network became unstable; slow connection and would lose internet access. 

I then swapped Unit 1 and 2 physical locations and had the same results. The network appeared more stable but speed dropped to ~1mb/s. 

I then unplugged the ethernet to Unit 1 (new slave/old Master) and the network was stable and around 13mb/s. 

Our old ISP was 20mb/s and with the two Deco M4s wired to the router/switch which was wired to the modem, we had 20mb/a everywhere. 

Our new ISP is 60mb/s and the deco net work never exceed 20mb/s. The wifi network from the modem/router/switch is 60mb/s pretty much anywhere in range and to all wired devices. 

I need to get this fixed. I was looking at adding two more M4 or M5 to increase the range into the backyard but right now I'm going to hold off until this is resolved. 

@TP-Link, 

I can confirm that with either Unit 1 or Unit 2 as master, the second unit cannot be plugged into ethernet or it will create an unstable network which will eventually block access to the internet.

Ethernet cables are tested and fine. 

Are there any ports I should open or other configuration changes I should make on the Helix Fi (gen 2) that the Deco M4s may require? 

Thank you for your help. 

@TP-Link, 

Thanks again for the quick responses. I'll get a stand alone switch and give that a shot. Hopefully I could find something in the next couple of days. 

Thank you @TP-Link !!! 

Picked up a TP-Link gigabit 5 port unmanaged switch today. Turned everything off while I hooked everything up and then powered things on. Was blinking red for a while and then it all came back online. Full ISP speed on wifi anywhere in the house. 

Time to pick up more Deco M4 nodes!