Outgoing IAX2 connections don't work on Mikrotik

RouterOS General
1

I have two Asterisk servers in two different networks, both behind LAN.
These servers are interconnected using IAX2 protocol.
UDP port 4569 is forwarded on both ends.
Router on one side is pfSense.
Router on other side was windows machine.

After I replaced this windows machine with Routerboard 951G-2HnD outgoing IAX2 connections stopped working. People from network that is using pfSense can call me, RouterOS perfectly forwards all IAX2 traffic. Amazingly, there is no outgoing connection to the server that is behind pfSense router.
If I unplug my Routerboard and plug in old windows machine - everything works.
All other connections work perfectly, including SIP connections.
I’ve tried RouterOS 6.6 and 6.7
Turning port forwarding rules on/off didn’t help.

2

I was able to set up SIP connection to remote server - works well.
IAX2 calls from remote server work well to.
But no IAX2 from my network to remote network.

3

Looks like there was some kind of incompatibility with pfSense.
It helped to switch firewall optimization to ‘conservative’ and disabling PF scrubbing in pfSense.

4

I have two different asterisk PABX using IAX trunks and IAX peers, and multiple IAX clients all behind Mikrotik routers and I never had a problem.