Frequent link down / up between two Mikrotik routers

My main router is an RB2011UiAS-2HnD-IN that acts as a DHCP server and has most devices connected to it. This is connected to a RB911G-5HPacD that provides 5GHz WiFi.

The wifi & eth ports of the RB911 are bridged and the two master ports (2 and 5) are bridged on the RB2011. All other ethernet ports on the RB2011 are slaves to 2 and 5 (as is the default configuration).

My problem is that the interface that connects the RB911 and RB2011 frequently goes down (and then immediately back up) for no apparent reason. This only happens when I’m trying to download files from a device connected to the RB2011 (happens with any device, including a btest directly to the RB2011 from my laptop on the 5GHz WiFi of the RB911). Transferring data from a device on the 5GHz network works without any issues.

Example iperf (laptop on RB911 WiFi to device connected via ethernet to RB2011):

------------------------------------------------------------
Client connecting to media, TCP port 5001
TCP window size:  129 KByte (default)
------------------------------------------------------------
[  5] local 10.0.2.7 port 50349 connected with 10.0.0.88 port 5001
[ ID] Interval       Transfer     Bandwidth
[  5]  0.0-11.2 sec   896 KBytes   653 Kbits/sec

During this time, the link between the two routers goes down.

Example iperf (device connected via ethernet to RB2011 to laptop on RB911 WiFi):

------------------------------------------------------------
Client connecting to 10.0.2.7, TCP port 5001
TCP window size: 32.5 KByte (default)
------------------------------------------------------------
[  3] local 10.0.0.88 port 48381 connected with 10.0.2.7 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   215 MBytes   180 Mbits/sec

Config files

Any help would be greatly appreciated!!

Setting

frequency-mode=regulatory-domain

,

country="united kingdom"

and

antenna-gain=4

seemed to resolve the problem! Don’t ask me why…