I have the same hw-config than you. Would you mind, posting your software-config - especially which driver+firmware you use?
Unfortunately I have many trobules as you can see here: https://forum.test.turris.cz/t/wifi-wlan-5ghz-trouble-mikrotik-bit-rate-tx-24-mbit-s-20-30-mbit-s-throughput/6041/10
Which output do you get here:
cd /sys/kernel/debug/ieee80211/phy0/ath10k && cat fw_stats
Thank you very much.