Primary uplink status change MX64 every 10-15 minutes

[ManolisFr]

First of all

We had purchased Meraki on August 2018. In the beginning we had 2 simple ADSL Connections 24Mbps connected in it (bridge mode) 

On february 2019 we changed the one of the above with  a new VDSL Connection 200down/20up from a Greek Provider .

The provider of the VDSL Connection gave as a Technicolor DGA 4130 and i changed it to bridge mode

Till June we had no problems with the load balancing.

After lot of disconnections on June i changed the technicolor with a TP LINK 9970 modem router in bridge mode and the problems disappeared..!!!

But..The provider didn't found problem on our telephone line and on Technicolor.. so i setup again technicolor which worked fine till yesterday..

Yesterday i made a firmware update on Meraki ( MX 14.40 ) and the problems appeared again. Till yesterday evening had this event every 5,10 or 15 minutes 

I didn't came back to tp link because it has no sip port for the telephone line (fax) but i am planning to do it tomorrow

[SoCalRacer]

Can you possibly roll back the firmware upgrade and check if you see the same thing?

[ManolisFr]

How can i do it?

Edit

I done it. I will check if the problem remains

[ManolisFr]

I roll back the firmware and i had already one disconnection

Till yesterday (before upgrade to the last version) i had

The 200Mbps/20mbps connection to internet port (which is 1Gbit) and 

The 24Mbps/1Mbps connection to Lan4/wan port

But i changed the ports. 

I wonder if the problem appears because the VDSL 200Mbps is on a 100Mbit port and creates bottleneck? ...

Or

I have the VDSL Connection which is static to PPPOE DHCP Mode on Uplink Configuration..Maybe i must set it to static mode?

[PhilipDAth]

Are you NATing anything into your site? If not, perhaps try not using bridge mode.

[ManolisFr]

The VDSL Connection is static. I have a port forwarding rule which allow an external wan ip to have access to my sql for downloading orders from our b2b site

It's 9:00 am now in Greece. I had the last disconnection before 4 hours . It seems to be ok now with the Technicolor modem but...

Why not using bridge mode? How can i make the load balancing?

[ManolisFr]

Till now (from 05:00am this morning) i had 5 disconnections/reconnections.

So i changed the technicolor modem router with a tp-link we have for backup reasons, and i have no disconnections again.