ath10k supports monitor mode. Recommended firmware version for a sniffer is 10.1.467.2-1. Also use recent enough wireshark which supports 11ac.

To tune into 80 MHz channel, in this example channel 36 (5180 MHz):

ip link set wlan0 down
iw wlan0 set type monitor
ip link set wlan0 up
iw wlan0 set freq 5180 80 5210

To capture HT40+ on channel 36:

iw wlan0 set freq 5180 40 5190

• Assoc Request frames not captured (Assoc Response shows up fine)
• cannot see Add BA action frames
• frames do not come up with FCS value in them
• the management frames do not contain mac timestamp as data/control frames