Hello. I have installed SXT Lite5 ac instead of SXT Lite 5 and have a bug.
When Channel width 20/40/80Mhz Ceee Band 5Ghz-only-AC is selected Tx Rate is dropping from 780Mbps to 6Mbps all the time with packets losts.
When I use 20/40Mhz Ce 5Ghz-only-AC then Tx Rate is dropping much seldom from 360Mbps to 6Mbps.
No Tx Rate dropps are only when using Band 5Ghz-only-N 20/40Mhz Ce.
I have uploaded the video illustrating this bug.
https://puu.sh/AiRJT/e42ae286a7.mp4
I used also Freq.Usage and Scan tool to check for interferences. But all is clear.
RouterOS and firmware versions are 6.42.1 on both SXT Lite ac.
Same is on RouterOS 6.40.8.

TDMA period auto drops packets. But TDMA period size 4ms fine.
I set TX power on both devices to 10dBm (13dBm MIMO? ). In this configuration TX/RX signal streinght is -45/-45.

TX Rate doesn't drops more from 780Mbps to 6Mbps. Just from 780Mbps to 702Mbps.

Is TX/RX signal streinght is -45/-45 safe for devices?

Im having the same issue in 802.11 also. any suggestions to solve it

That mp4 cannot be found: That puush could not be found.

Check wireless "registration" , all fields. (detail mode in winbox), when testing different settings.
- # of frames compared to # of hw frames (how may retransmits?)
- what is the hw_retries setting (retransmits not counted as failure, not lowering the MCS. MCS (interface data rate) is stepped up and down, it should not jump from max to min)
- CCQ
- P throughput
- SNR (-45dB RSSI is ok, SNR should be good as well)
- 6Mbps is the speed for all broadcasts/multicasts. (Will be seen a lot if there is no unicast load on that link)
- also use "Snooper" for finding other transmitters. (Scan only shows AP)
-ac-only highest MCS(MCS09) , 80 MHz, is much more delicate than highest n-only (MCS07/40 MHz)
- 6.42 is too old as RouterOS. Go for 6.45.9 LT , or 6.46.6 Stable (6.47 is a .0 release, a bit unstable).