First I've made the following modification in the /package/kernel/mac80211/files/lib/netifd/wireless/mac80211.sh :
mac80211_interface_cleanup() {
local phy="$1"
for wdev in $(list_phy_interfaces "$phy"); do
ip link set dev "$wdev" down 2>/dev/null
# iw dev "$wdev" del
done
}
That disables to remove the interface and the AP may be created than. The rest modifications with ifconfig and iwconfig were used only for disabling and restart of the interface and are not important for debugging.
But this is working only with kernel 4.14.72 and older. The newer one results in kernel panic as described here: