Now with uptime only 22days. P2P link is locked to 6,5Mbit. Customers call - speed is terrible 
note: you need inspect Last Measured times on client not on AP
Yes but what is solution? In configuration P2P links is problem on AP side. Disable/enable wireless solve this problem.
When you have locked clients - what is solution? Reboot (Disable/enable) AP or just reboot client?
to ‘unlock’ the client it is enough to disconnect it. Use the [-] (the minus) button in Registration table in winbox (either on AP or on client). This way the client reconnects in shortest time probably.
I know it. But this is not solution of problem 
Have you any news? A have this issue now in P2MP scenario. AP is rb800 with 5.26.
Some clients are locked on 9Mbit on TX. Very bad throughput
nothing new. I have many lockups on clients using RB1xx boards but newer boards have the problem less frequently. And it looks when we monitor them they lock the modulation even less frequently
I is not only problem rb1xx. I have the same problem on rb411 and Groove. It is SW problem
we have the same problem with RB800. So far, the problem is solved by restarting but it is repeated every week and there is no solution for the problem yet.
Today I will upgrade to 6.5 and see if there are results.
With 6.5 the same issue. Today reported to support
Out of interest, have you tried setting all of the following to an empty string on both client and AP:
basic-rates-b
supported-rates-b
basic-rates-a/g
supported-rates-a/g
Just an idea because 6Mbps seems to be listed as an 802.11a/b/g rate, not an 802.11n-like HT rate. Also, I’ve removed all the a/b/g rates from a client/AP pair and the 6Mbps rate is still listed in “/int wire reg print stats”. This might suggest that if you’re only looking at the “Signal Stengths” table then the “6Mbps” won’t ever go away… Maybe MikroTik can confirm that the 6Mbps rate is tested for signal strength regardless of your data rate settings?
Along the same theme, if your link ‘usually’ has a data rate of 130Mbps, with a high CCQ, then why not use “rate-set=configured” and explicitly limit your data rate choices to HT20-7 or HT40-3 or whatever. Maybe that will stop RouterOS from even picking the 6.5Mbit rate? (By the way, 6.5Mbps is HT20-0, not the 6Mbps a/b/g rate in case there is any confusion)
I have two test OmniTiks running NV2 locked to mcs-11 (ht20-3 and ht40-3) and although the 6Mbps rate shows up in signal strengths, the actual tx/rx rates are both 120Mbps:
[admin@MikroTik] /interface wireless> reg pr stats
0 interface=wlan1 radio-name=“D4CA6DF04D3B” mac-address=D4:CA:6D:F0:4D:3B ap=yes wds=no bridge=no rx-rate=“120.0Mbps” tx-rate=“120.0Mbps” packets=79097,106164 bytes=24039103,143155344 frames=25726,101470 frame-bytes=24160704,142808304 uptime=9m1s last-activity=0ms signal-strength=-29dBm signal-to-noise=85dB
signal-strength-ch0=-45dBm signal-strength-ch1=-29dBm tx-signal-strength-ch0=-45dBm tx-signal-strength-ch1=-42dBm strength-at-rates=-29dBm@6Mbps 0ms,-41dBm@HT20-3 8m20s130ms,-42dBm@HT40-3 0ms tx-signal-strength=-40dBm tx-ccq=100% rx-ccq=100% distance=1 routeros-version=“6.2” last-ip=192.168.88.223 tdma-timing-offset=-1
tdma-tx-size=1520 tdma-rx-size=4000 tdma-retx=0 tdma-winfull=0
[admin@MikroTik]Hope this helps… do report back!
Hello. I have renamed topic. Yes, it is 6,5Mbit. When I have mode - 5Ghz-only N. The problem is the same - locked to 6,5Mbit after some time…
You have nice idea. 
Using only higher MCS rates, other disabled. I will try it on P2P links. But this is not solution for P2MP where is the same problem with locked modulation on 6,5Mbit
Ive had this problem. I can add just a few bits of info:
1/ When problem occurs, to resolve it no reboot is needed. Just disconnect the wireless client and when it reconnects it’s solved till it happens again!
2/ Problem is not solved by not allowing 6.5mbps rate. It just locks on the higher rate as well.
3/ Problem is pretty rare. Probably has happened only a handfull of times over a year on two of 20 links.
yes, I can confirm everything you wrote.
Now we have no problem with 6.5 and 6.6.
you are a lucky man, then. It is only matter of time when the links will lock. We have had already several locked modulation cases on 6.6. Finnally it happened that Mikrotik support staff was able to see it on live so they installed some debug pakage on the radios and rebooted them. We were lucky because after it the radios locked the modulations again soon. But Mikrotik’s were not able to get all needed information out of the radios probably - because they compiled a new wireless package and rebooted the radios again. And the link didn’t lock after it yet.
After observing the problem - there is an interesting thing related to RB1xx - I started to upgrade them to 5.26 and after it the rate of problems with these old boards significantly lowered
bad news
We can only test the 6.7 and hope …
I am creating a script to check this. I wont have time to test for a while it but if anybody can try this let me know if it works, the script would need to go both ends to work or change it to check rx-rate too on one end:
{
:local a [/in wi reg get number=0 tx-rate]
:put $a
:if ($a>=6.5Mbps) do={
/interface wireless registration-table remove 0
}
}
if you want to detect the problem without too much false positives you really have to:
- check it on stations not on APs (the registration table on station shows that only one or 2 modulations were used for long time - other modulation have high ‘uptime’)
- accept the fact that the locked modulation can occur on other modulation than 6.5mbps. Probably it could be any modulation (even the highest one)
- be sure that there is enough traffic - because with no traffic any link tends to fall down to 6.5mbps for longer time
- you will probably need to use no Mikrotiks’s CLI scripts but some external scripts which connects to stations via API
I think in my case this will work as it’s a point to point backhaul link.
- check it on stations not on APs (the registration table on station shows that only one or 2 modulations were used for long time - other modulation have high ‘uptime’)
I did say both ends or change script to check tx and rx.
- accept the fact that the locked modulation can occur on other modulation than 6.5mbps. Probably it could be any modulation (even the highest one)
Ive never seen it happen at higher rate apart from when I disabled the 6.5 one as a test. I think that would be good enough at least for my setup to solve it.
- be sure that there is enough traffic - because with no traffic any link tends to fall down to 6.5mbps for longer time
It never drops to 6.5Mbps unless there is the problem apart from maybe a minute or two when it first connects. But your right that’s something else to think about.
- you will probably need to use no Mikrotiks’s CLI scripts but some external scripts which connects to stations via API
that’s an option but a real pain in the ass to setup just to work around some bug :-0