Looks like I have to answer to myself.
So apparently NV2 doesn’t work so good in noisy environment with a lot of clients. But to cut lower MCS and rates is a good move, just need to correlate respective speeds.
This is the same mount place, another AP with even more CPE (34) switched to nstreme. As for now CPE are stable, uptime more than 1 hour without disconnects.
/interface wireless
set [ find default-name=wlan1 ] adaptive-noise-immunity=ap-and-client-mode ampdu-priorities="" band=5ghz-onlyn basic-rates-a/g=24Mbps,36Mbps channel-width=20/40mhz-Ce country=no_country_set \
default-forwarding=no disabled=no frequency=5320 frequency-mode=superchannel guard-interval=long hide-ssid=yes ht-basic-mcs=mcs-3,mcs-4,mcs-5,mcs-6,mcs-7 ht-supported-mcs=\
mcs-3,mcs-4,mcs-5,mcs-6,mcs-7,mcs-9,mcs-10,mcs-11,mcs-12,mcs-13,mcs-14,mcs-15 hw-retries=4 keepalive-frames=disabled max-station-count=40 mode=ap-bridge multicast-helper=disabled \
nv2-cell-radius=10 nv2-downlink-ratio=65 nv2-mode=fixed-downlink nv2-preshared-key=password nv2-security=enabled preamble-mode=long radio-name=SECTOR2 rate-set=configured scan-list=\
4920-6100 ssid=SEC2 supported-rates-a/g=24Mbps,36Mbps,48Mbps,54Mbps tdma-period-size=auto vht-basic-mcs="" vht-supported-mcs="" wireless-protocol=nstreme wps-mode=disabled