For Ath10k, 18.06.x is fine for the AP/VLAN interface mode, but not 19.07.0 / 19.07.1
There seems to be some more info on the -ct bug, and a rebuild to non -ct firmware would likely resolve.
NerdyProjects posted a commit to OpenWRT that seems related
commit 92953ae99f240a0b45ab66defde5f7b8eeb94e35
Author: Koen Vandeputte <koen.vandeputte@ncentric.com>
Date: Tue Sep 24 11:58:54 2019 +0200
ath10k-ct: update to version 2019-09-09
5e8cd86f90da ath10k-ct: Backport ap-vlan code from 5.2 to 4.20 and 4.19 drivers.
0c518586bd7f ath10k-ct: Fix a few warning splats.
Adds AP VLAN.
Refreshed all patches.