I had to downgrade to ~2 years old RouterOS to be able to connect to 5 GHz network.

what version did the trick?

Same here, connecting to Archer C6 with this error. I'm using RB333, AR5413, 5Ghz A, RouterOS 6.47. Interesting thing is that I replaced ancient RB532 with 5.26 firmware, which was able to connect to this wlan without any issue. Also, when I set the interface to wds slave, it is able to briefly conn...

what has been seen cannot be unseen :O