Usually, when I used an acl mac filter, I've tried to connect to my wifi station with a new device, saw a new MAC address in logs, and then was adding it to mac list in /etc/config/wireless.
I was surprised when have not seen any messages like "Station- not allowed to authenticate" or something in logs. It took me a few time to understand that it does not work now.
Ok, I tried to change debug level in file /lib/netifd/hostapd.sh (level 0) and... unfortunately, an unknown device refuses silently.
I exactly remember that it was working in version 18.06.0 and LEDE.
Current version 18.06.5, r7897-9d401013fc