LAN and internet traffic running over zerotier

Two macs.
Same subnet.
Different subnet (no overlap) than zerotier.
One is plex server, other is laptop.
Never had problem before, recently things got very slow with the plex server.
Internet speed test (netflix’s fast dot com) on one computer (the 10 year older one) is much faster than the plex server (brand new hardware as of 2020).
Both are on same LAN and plugged into same switch.
I noticed the plex server was reporting the client IP as the zerotier IP of the other computer rather than the lan IP.
Plex server (the problematic computer) is running ZT 1.8.4.
The older computer (never had a problem with zerotier before) is running ZT-cli 1.2.12.
Both are running Mojave 10.14.6 with latest patches.
Both are ethernet (no wifi).

I’d proactively send a dump to Grant but profile is private and their doesn’t seem to be an option.

Of course I have tried reboots and other things without any luck.
I’m using the default config as it was installed.
Any ideas other than uninstalling zerotier?