Intro: 

The Issue started from day one of use. I have 3 units, my ISP modem, My plan is 1 GBS. Tested directly connecting my laptop to the modem.

First the connection drops which disconnects all my calls.
Upon checking the app I can see the classic Abnormal Wan Port Speed message. Speedtest shows speeds up to 90 mbit. Maybe 3-4 times a day
 

Prior fixes:

1) Fix 1: Rebooting occasionally helped, but the issue persisted multiple times a day.

2) Fix 2: Rebooting and reconnecting the lan cable between my main deco and ISP modem to a different port - also helped short term
3) Fix 3: replaced the standard TP link cable that connected my Main deco to the modem with a brand new Cat 6 - Problem was NOT solved

4) Fix 4: replaced with a shielded Cat 6 cable - Same as before

5) Fix 5: promoted my other Deco to the main, swapped their positions. Now here is some progress.
The issue persists, however Deco switches to 100 mbits and then after 20-30 min back to 1 gb by itself and less often. maybe 1-2 times a day, sometimes not once in 2-3 days if I track it.

This is still not acceptable.

My last try is probably: testing for any noise from the power outlet, which is ridiculous. I hear that the problem is with the firmware and some people we able to receive installation file for an older firmware which fixed the issue.

Any suggestions? Could not find any on this forum so far....