Why doesn't the zoiper in the queue often call?

Question

Asterisk

Colleagues, there is such a problem.

Asterisk 11.25

Clients -- softphones zoiper and 3cx
When a call arrives in the queue, the ringing agent status on the aster itself is in the queue. sngrep shows that softphone invites are flying. But at the same time, the softphone itself does not react in any way.
There is no system, because sometimes the call goes through.

Softphones are located with the PBX in different subnets, connected via VPN, without NAT, just routing.

Has anyone come across such a problem?