Windows 10 > Rpi connectivity - how to debug?

Hi,

The nub of this problem is that with Zerotier running one of my Window machines is experiencing problems using some local subnet addresses (not the zerotier ones)

I am migrating from one windows 10 system to another.
they are both running zerotier. With the older one, I can connect to a Raspberry PI via http ; with the other I cannot unless I stop Zerotier. I can connect to other Raspberry Pis correctly.
The difference is that the RPi refusing connection also runs zerotier. The problem is only solved by stopping Zerotier on the Win PC, not by stopping zerotier on the RPi.

I hope I’ve managed to describe the problem adequately.

Anyone with any debugging ideas?

Thanks!

B.