unstable ping with nstream

Hi all,
I figured out when the ping problem starts but I still can’t find out what’s causing that problem and how can I solve that. I have routerboard 443 and 2x cm9 cards are in that RB (2 links for 2 different towns). Here’s the thing: I’m pinging both links, wlan1 and wlan2, and ping is unstabile as I described in my previous posts. After disabling wlan2, ping that goes through link wlan1 is 1ms and it’s stabile. That’s ideal but as soon as I enable wlan2 ping is broken again. An that’s happening only when nstream is on.

If I enable wlan2 and set him on frequency which is not available to client, then client cannot connect and ping to wlan1 is ok, which means that soon as someone is associated on wlan2, ping to wlan1 is broken.

RB433
ROS 3.20
CPU USAGE: 17%
Trafic on link: ~1Mbit

Wlan2 enable:

Wlan2 disable: