WAN Interface Bouncing

[ZDonaldson]

I have been struggling for months with this one:

We have (2) internet connections.  Our primary internet connection disconnects every other monday between 11:24 am and 11:30 am.  It is acting as if it is on a regular schedule of some sort.  

The internet is fiber with an ethernet handoff from the provider.  I am splitting the connection between our primary and hot spare MX units with an 8-port switch.  I am doing the same with our back up internet on a separate small switch. I've swapped the small switches to ensure they aren't the issue, the problem stays with the primary internet connection.  

Cables have been changed.  A ticket with the ISP was opened, they found nothing.  

The dashboard log shows this:  

Appliance status

Primary uplink status change

uplink: 0

I haven't been able to confirm with support if this event means the interface has lost physical link or if one of the internet connectivity tests has failed which is failing over the internet.  I am guessing its a physical link loss because it fails back over to the primary almost immediately.

I'm at my wits end on this so I will take all ideas.

[alemabrahao]

Is the link connection directly connected to the MX or do you have a switch between the ISP Router and the MX?

Honestly, it doesn't seem like an MX problem.

[PhilipDAth]

I also doubt this is an MX issue ...

But let's try and break the problem down further.  Perhaps next Monday, can you plug the MX circuit directly into the primary MX (this will obviously mean your warm spare is not working).  This will bypass your switch, and a couple fo connections.

If the issue still happens, you know it is directly related to the ISP and primary MX (since everything else was not plugged in).

Does the uplink graph in the dashboard show any big traffic flows at this time (perhaps someone is doing a big upload/download).

This is the list of things monitored on the uplink:
https://documentation.meraki.com/MX/Firewall_and_Traffic_Shaping/Connection_Monitoring_for_WAN_Failo... 

Ask Meraki support to confirm which event is causing the failover.  Perhaps it is the link going down.  Perhaps the link is staying up, but the tests are failing.