Packet flooding and high CPU usage

I'm trying to create a basic ZT path between two buildings. Each building has a OPNsense 18.1.9 edge router with the ZT 1.2.8 plugin installed.

Building A: LAN 192.168.2.0/24 - ZT 192.168.5.2
Building B: LAN 192.168.3.0/24 - ZT 192.168.5.3
ZT: 192.168.5.0/24
3 ZT managed routes: one for the ZT network, and one for each of the building LANs with the their respective ZT IP listed as their respective gateways.

The two OPNsense nodes are the only nodes in the ZT network. Both have bridging enabled, and auto-assign IP disabled. Flow rules in my.zt are all default. Network is idle other than a Windows box on one building's LAN pinging a Windows box on the other building's LAN (less than 2KiB/sec)

ZT is generating a MASSIVE amount of packets that is spiking the CPU to 100% regularly, yet the packets never go anywhere, and they're not generated from any of the nodes on either network. When this CPU spike happens, all connectivity over ZT is entirely dropped.

Reference: https://drive.google.com/file/d/1NIkdnilV0HSXuytMPn3zHzragyAcEa33/view?usp=sharing

You can see in the screen shot from the OPNsense interface stats that ZT has generated over 600GiB of content total, yet WAN has only transfered around 35GiB and LAN only 21GiB. These stats are for around a 24 hour period.

Nothing is matching the ZT network at all in pfTop or Firewall log, so at this point I'm not sure where next to investigate this particular issue?

Start with the OPNsense interface statistics and reproduce the idle two-building setup described in the report. Compare ZeroTier traffic with pfTop and the Firewall log, then trace the unexplained packets against the managed routes, bridging, and flow rules. Done means identifying the packet source or path, preventing the flooding, and preserving connectivity during the test.