I struggled for a long time with WiFi multicast. WiFi multicast transmits at a low, fixed data rate that is only sometimes configurable, and there's no link level ACK. This was acceptable back when WiFi had a small set of data rates but it is completely unusable now beyond the occasional ARP or mDNS query. Anything more will bring a base station to its knees. The best workaround is multicast to unicast conversion, where the base station sends a separate, acknowledged copy to each group member at whatever data rate its link can support. Because this may involve retransmissions, the latency can vary. You can tell if a base station is performing multicast-to-unicast conversion by looking at the frames received by the clients, e.g., with Wireshark. If conversion is being done, the Ethernet destination MAC address will be that of the client station, not the Ethernet multicast destination address in the originated frame. The IP header will not be modified, so it will still have a multicast IP destination address. It's ironic, but radio is rapidly losing what used to be its defining property: the ability to broadcast to arbitrarily large sets of listeners within an area. Spatial reuse, multi-access contention, rate-adaptive links and directional antennas (especially MIMO) are all valuable for increasing spectrum efficiency, but they've turned radio into a large set of point-to-point links.