Essentially, this is what has to be done on 19.07.2 to follow up on the answer from @fantom-x:
opkg update
opkg remove ath10k-firmware-qca9984-ct kmod-ath10k-ct
opkg install wget ath10k-firmware-qca9984 kmod-ath10k
cd /lib/firmware/ath10k/QCA9984/hw1.0/
mv board-2.bin board-2.bin.bk && mv firmware-5.bin firmware-5.bin.bk
wget -O firmware-5.bin https://github.com/kvalo/ath10k-firmware/raw/master/QCA9984/hw1.0/3.9.0.2/firmware-5.bin_10.4-3.9.0.2-00086 --no-check-certificate
wget https://github.com/kvalo/ath10k-firmware/raw/master/QCA9984/hw1.0/board-2.bin --no-check-certificate
If you wish to apply this fix, this is what you would have to run in the CLI, then reboot the router. Just paste it line by line.
EDIT: Updated to include substitution of kmod-ath10k-ct also that I mentioned on this post.