Random WAN Drops

Question

I recently migrated my UTM over from an older VMWare ESXI platform (5.5) over to new hardware and the newest version (6.7). 
 Since doing so, I've been having what seems to be random WAN drops and I can't figure out why. My physical connectivity was: 
 
 Verizon FiOS ONT -> Dell Server EN0 ethernet port 
 Within ESXi, I have EN0 configured in a port group on a vSwitch with only the WAN interface of the UTM included. This is the same way it was setup on my ESXi 5.5 box and worked perfectly for years. Now, my WAN is seemingly randomly dropping out. I've searched through the UTM logs and can't find anything solid indicating a problem, however I do receive emails saying prefetch failed or spam filter can't reach the database servers, or that the WAN is offline/online. 
 I started at Layer 1, changed ethernet cables. Then I routed my WAN connection through a separate VLAN on my cisco switch. The new (and current) topology is now: 
 
 Verizon FiOS ONT -> Cisco Switch -> Dell Server EN0 ethernet port 
 The WAN has dropped multiple times since then with notifications coming through email. Cisco server logs show no Layer1/2 disconnects. I think this drop is coming in a higher layer in the stack. When the problem has occurred, within the UTM dashboard, I have never seen the WAN interface show disconnected, however it seems that after I refresh the lease on it, it drops for a few seconds, then pulls the same IP again and everything works. I have also noticed a few times on the uplink monitoring tab that it will say WAN OFFLINE. I turn uplink monitoring off globally, then back on and it resets to WAN ONLINE and everything works again. 
 Any pointers as to what I can look for to pinpoint the problem? I could backup the UTM and re-install, but I'd really like to figure out what's causing this instead of just blowing everything away and not really knowing if the problem is fixed or not. 
 I'm running 9.605-1 UTM build 
 Hardware is a Dell R720 server. 
 Midway through trying to post this, I lost the WAN again. This is getting old!

Tango2 · Answer

Knock on wood... I think I figured it out. Fingers crossed that it's fixed now. Hopefully someone else can benefit from what I found. 
 The Dell R720 (and many other "servers") offer IPMI or in this case iDRAC which is an in-band management platform to see a remote console over IP among other things. My configuration wasn't right, and it was fighting for an IP on the same physical interface as my WAN interface on my UTM. I found this via the packet capture that I performed on the physical interface. I noticed traffic originating from two different MAC addresses (the virtual MAC on the UTM as well as the virtual address of the iDRAC controller). I immediately checked the settings and noticed it was pulling IP addresses from my ISP as well, which was conflicting with the IPs I was pulling on the WAN of the UTM. 
 I'm 99% sure this case is closed, but I'll monitor for the next day or two and see what happens.