Zerotier behind opnsense 2 NAT

[Mann-IT]

HI Pros,

I use a lot of Servers behind Opnsense with Zerotier Clients on it.
Now my Problem is Zerotier does not really work fast if it is behind 2NATs. This cannot be changed.
Because then there is no direct connection between both zero clients and then he will route over Zero Global server and this ist really really slow.
My problem is, I oppend all int Firewall and see no Blocks ind Firewall. But the Clients will not connect direct.
Has someone the same problem? An better an fix?

Greetings MArio