Zoom VRC and SIP calls

[noncidomai]

Hi all, We have a complex Zoom infrastructure with on-prem VRC and load Balancer.
I'm trying to perform SIP calls to 3rd party virtual room (pexip).

If I call from a client NOT in my LAN (PC or mobile) I can do this using the "Call a room" option. If I do the same from a LAN client (basically able to reach VRC server) call doesn't work. If I make VRC unreachable (by simple ACL) to the same client, call success.
It seems that zoom client always try to use VRC for SIP calls. Is this normal?

And why SIP calls does't work even if VRC is able to reach internet?

thank you