Hello All
I just need so HELP iv came across this issue on few Mikrotik LHG XL AC rbs.
Upgraded ROS to 6.40.8
Issue: Nothing can be done on LHG Cannot change any wireless settings or do Freq change. Cannot upgraded or downgrade ROS either. Each time a person tries to make any change to device on On Bridge side the device kicks and out and almost like it reboots but it does not but takes around 5mins to come back online iv experienced this with 3x brand new LHG Ac units.
Have you tried to netinstall…could maybe be a bad firmware download?
that is next step just wanted to find out if other guys seen this as well
i have exactly the same issue on a LHG G-5acD 
even on the std firmware could only change the settings once then no go after that u have to reset it to make changes and do it right otherwise reset again lol
Yes thats exact same im getting u jst allowed to change it once when u setup. Should i return the device to scoop
@tafseer wil maybe be able to help think he had the same issue
@tafseer had to load 6.43rc42 as it seems to be a problem on lower ROS versions, dont know if @spin approves maybe he can shed some light as well.
Came across the same issues and still struggling with the clients link.
i would load the latest ros via net-install if i had the rb then if it does not work take it back my one is at a clients house so don’t have it play with and see what happens
i also think it is to do with the ARM Ros on the AC models
The problem occurs only once the wireless settings have been applied. Thereafter, changing wireless settings, results in the rb rebooting. Problem is due to the buggy ros preinstalled with the device.
To fix, perform the following steps:
Note: Spin will need to advise if Ros6.43rc versions are acceptable.
Thank you @tafseer im going to try that tonight
This fix works 100% iv been struggling for 3 weeks 
Main issue i had could not change wlan settings
Client could access Audi but not download from it
After applying fix on both sides everything is working 100%
Thank You very much guys
Can you guys let me know where the bug is fixed? Or when the bug is fixed in main. I will see if I can skip the version check for these.
Yip All Mikrotik AC Lhg’s and AC Sxt’s using arm’s seems to have the same problem…
https://forum.mikrotik.com/viewtopic.php?f=7&t=128916&sid=3d91c446e4642c1f12af53d696c07eb1&start=50
Wow check this out lol 
We are close to a solution to the Nv2+ARM performance issue, please hold on for a day or two, when we will release the changes in RC release chain, for first testing.
That was more than a few days ago…
We did make changes, tested them, they were not enough, so we continue testing, so that the release has a bigger impact. We want the fix to be good for everyone.
rc45 contains Nv2+ARM fix. It will be released within the next 24 hours.
What's new in 6.43rc45 (2018-Jul-17 08:30):
MAJOR CHANGES IN v6.43:
----------------------
!) api - changed authentication process (https://wiki.mikrotik.com/wiki/Manual:API#Initial_login);
!) backup - do not encrypt backup file unless password is provided;
!) btest - requires at least v6.43 Bandwidth Test client when connecting to v6.43 or later version server except when authentication is not required;
!) cloud - added IPv6 support;
!) cloud - added support for licensed CHR instances (including trial);
!) cloud - reworked "/ip cloud ddns-enabled" implementation (suggested to disable service and re-enable after installation process);
!) mac-telnet - require at least v6.43 MAC Telnet client when connecting to v6.43 or later version server;
!) radius - use MS-CHAPv2 for "login" service authentication;
!) romon - require at least v6.43 RoMON agent when connecting to v6.43 or later RoMON client device;
!) webfig - improved authentication process;
!) winbox - improved authentication process excluding man-in-the-middle possibility;
!) winbox - minimal required version is v3.15;
----------------------
Changes in this release:
*) ethernet - improved stability when changing ethernet interface L2MTU on CRS328-24P-4S+ (introduced in v6.43rc11);
*) ipsec - improved invalid policy handling when a valid policy is uninstalled;
*) lte - added additional ID support for SIM7600 modem;
*) sfp - fixed default advertised link speeds;
*) vrrp - fixed VRRP packet processing on VirtualBox and VMWare hypervisors;
*) winbox - properly display all flags for bridge host entries;
*) winbox - show "System/RouterBOARD/Mode Button" on devices that has such feature;
*) wireless - improved Nv2 reliability on ARM devices;
And here:
*) wireless - improved Nv2 reliability on ARM devices;
Available on downloads:
https://downloads.ctwug.za.net/mikrotik/routeros/6.43rc45/
Hi Guys
Mikrotik release v6.43 stable on 06 Sept 2018. The change logs include the Nv2 reliability improvement as well. Could someone with an ARM AC router please update to this version and provide some feedback.
Please do not upgrade yet. See:
https://forum.ctwug.za.net/t/file-downloads-downloads-ctwug-za-net/9799/45?u=dizzle
I’ve fixed our radius server to work with 6.43. I’ve also updated our Housekeeping scripts to only accept 6.43 for AC ARM devices going forward. So you need to upgrade to 6.43 stable (and not use release candidate anymore).
Please upgrade your AC ARMs to this version.