could you tell us more about your setup on Hotspot/DHCP? Are you using Hotspot/DHCP on wireless?
Please make the support output file right after you see this log message and send it to support@mikrotik.com
Not sure how to do code so someone else can translate if they like but here’s what worked for me:
IP → DHCP Server → Leases → Add new → General=“Pool_Name”, MAC Address=“MAC address of desired blocked”, Server=“Name of DHCP Server”, Block access = yes, Address List = Black-list