Zerotier unreachable

Here is what I observe:

I have a zerotier network interface that get's an ip pushed and the routing entry is there.

In the firewall-config there is a zone with this interface.

The problem: I cannot reach other machines on my network (either with ping or ssh).

When I do a tcpdump on this interface I see no traffic at all - except when I try to ping another machine. Then I see arp-requests on this interface.

I am not a network-expert and I have no clue at all how zerotier works. My problem is that I cannot reach my other machines anymore and I am not in the mood anymore for further experimentation.

I am not running vanilla openwrt, so I am on my own here and I am giving up now unless you have a last idea what I could try.