ref https://archlinuxarm.org/forum/viewtopic.php?f=9&t=17095#p73046
I had the exact same problem. It seems to be related to the combination of some AP models and Raspberry Pi and is caused by a new feature which is supposed to lower CPU usage.
This worked for me as a workaround:
- Create a new config file "/etc/modprobe.d/brcmfmac.conf".
- Add the following line "options brcmfmac feature_disable=0x2000".
- Save and reboot.