host that virtualbox vm pfsense is running on drops connections

[adfhaerhad]

Set up:

• Host - Ubuntu 18.10
  ** Host has a total of 4 NICs (2 on MB, 2 on PCIe)
  *** The 2 NICs on the PCIe have static IPs of 0.0.0.0 for pfsense guest interfaces (NIC 1 & NIC 2)
  **** Both NICs are set to bridged in Virtualbox w/ adapter type "Intel PRO/1000 MT Desktop (82540EM)" in promiscuous Mode "Allow All"
  *** The other 2 NICs that are on the MB (NIC 3 & NIC 4) are set to DHCP for the Ubuntu host.
• Virtualbox Guest - pfsense 2.4.4-RELEASE-p2 (amd64)
• Switch is Netgear GS105 1 G

Topology:
ISP router > guest pfsense WAN (NIC 1) > guest pfsense LAN (NIC2) > switch > AP & back to host on MB NIC 3.

Problem:

• The host drops all connections intermittently, ping (hostname or IP), ssh, https, etc.
• Other nodes connected via AP are NOT experiencing drops.
• On the host, if I disconnect the CAT cable and connect the host to Wi-Fi, I don't experience any drops. I don't want the host connected via Wi-Fi due to double NAT issues.

Troubleshooting:

• I've switched out the cables to both the switch and to MB NIC 3;
• I've connected the host to MB NIC 4;
• I've tried connecting directly from NIC2 to NIC3/4, all had the same outcome.

Other Info:

• No power saving options are enable on Ubuntu host.
• Prior to setting up the virtualbox pfsense I had a SG-2220 that was connected directly to NIC 3 and never experienced drops like this.

Any ideas for additional troubleshooting as to why the host randomly drops?
What to look for in pfsense or on the Ubuntu host?