Yeah, in spite of the fact that there are 2 stacked switches, all the APs connected to 1 physical switch.
No other configuration on switch, all by default. I didn't have direct access to the switch, bank IT network engineer was preparing infrastructure for me and that's what he told me: "no special config, default".
I'll ask him to re-check the config once more, any recommendations except broadcast blocks, mac-limiting? May it be concerned with STP somehow?