ath10k for QCA9984 updated once again
Perhaps it fixes the issues described above?
"This release includes a new DFS host confirmation feature for better regulatory
enforcement. This means that, when using AP mode, DFS channels in FCC regulatory
region won't work without the corresponding ath10k patch:
ath10k: DFS host confirmation"
And a bit more info on this release: http://lists.infradead.org/pipermail/ath10k/2018-May/011376.html