I've come across a very specific, but possibly quite critical problem with MacBooks connected as clients to Mikrotik APs with WMM enabled/required, running the latest ROS 6.41 (stable). The problem seems to be located somewhere in the interplay of the Mikrotik WMM implementation using priorities and Mac OS. If I have the firewall set specific priorities (strangely enough only with 1, 3, 4, or 6) on packets that go out to the MacBook, the MacBook doesn't seem to be able to make sense of them. I can see them go through the sniffer on the AP, but either they don't reach the MacBook correctly or they get discarded there.
Now that I've written them down, there seems to be a pattern with the strange specificity of the numbers, though. 1, 3, 4 and 6 are precisely those numbers where the queue changes. At 1 (from 0) from best effort to low priority queue, at 3 back to best effort again, then at 4 to high prio, finally at 6 to top prio. It's too specific to be mere coincidence, I guess.
It should be possible to reproduce this behavior simply by setting up an AP with WMM enabled/required, bridge settings "Use IP Firewall" and "...For VLAN" both active, and a single firewall rule like:
/ip firewall mangle action=set-priority chain=postrouting new-priority=3 passthrough=yes
Test with all eight priorities (0-7), and the described pattern should emerge. By the way, iOS seems to be unaffected! I also don't think it depends on the Routerboard hardware, as for me the same problem exists on a hAP ac, a hAP ac lite and a wAP ac. I have also tested with two seperate MacBooks, both same behavior.
Maybe we have a real generic problem here and not some even more specific thing with my network. It seems so random. Maybe someone could try and reproduce this with their devices?