rbxxxx <--> ubnt1 <--> ubnt1 <--> rb1200 <--> ubnt3 <--> ubnt4 <--> rb1200 <--> PC Core <--> provider

On each node were some rockets m5 with sectors and many M5 CPE. Each node had OSPF. On Core router was nat for most of traffic and some srcnat and dstnat rules. Some customers were complaining about disconnecting networks games, VPN and VoIP sessions. After failure, setup on this part of network was changed

PC Core router <--> ubnt1 <--> ubnt1 <--> ubnt3 <--> ubnt4 <--> provider

The only thing that was changed is lack of rb1200's. No more disconnecting. We've found that problem occured on first 10 ports of rb1200. Problem was every ~20min. ROS from 4.xx to 6.xx. UBNT 5.5.2 and 5.5.4.