I too am having issue with an iPhone XS Max connecting to a HAP AC and HAP AC2 both running 6.43.2.
Macbook Pro, iPhone 7 Plus and iPad Pro all working fine.
Current Wifi Setup from the AC2:-
/interface wireless security-profiles
set [ find default=yes ] supplicant-identity=MikroTik
add authentication-types=wpa2-psk eap-methods="" management-protection=allowed \
mode=dynamic-keys name=main supplicant-identity=""
add authentication-types=wpa2-psk eap-methods="" management-protection=allowed \
mode=dynamic-keys name=guest supplicant-identity=""
add authentication-types=wpa2-psk eap-methods="" management-protection=allowed \
mode=dynamic-keys name=kids supplicant-identity=""
add authentication-types=wpa2-psk eap-methods="" management-protection=allowed \
mode=dynamic-keys name=iot supplicant-identity=""
/interface wireless
set [ find default-name=wlan1 ] band=2ghz-onlyn channel-width=20/40mhz-Ce \
disabled=no mode=ap-bridge name=wlan1-main security-profile=main ssid=ap1 \
wireless-protocol=802.11
set [ find default-name=wlan2 ] band=5ghz-n/ac channel-width=20/40/80mhz-eeeC \
disabled=no frequency=auto mode=ap-bridge name=wlan2-main security-profile=\
main ssid=ap1 wireless-protocol=802.11
add disabled=no keepalive-frames=disabled mac-address=BA:69:F4:33:5E:B6 \
master-interface=wlan1-main multicast-buffering=disabled name=wlan1-guest \
security-profile=guest ssid=ap1-guest wds-cost-range=0 wds-default-cost=0 \
wps-mode=disabled
add keepalive-frames=disabled mac-address=BA:69:F4:33:5E:B8 master-interface=\
wlan1-main multicast-buffering=disabled name=wlan1-iot security-profile=iot \
ssid=ap1-iot wds-cost-range=0 wds-default-cost=0 wps-mode=disabled
add disabled=no keepalive-frames=disabled mac-address=BA:69:F4:33:5E:B7 \
master-interface=wlan1-main multicast-buffering=disabled name=wlan1-kids \
security-profile=kids ssid=ap1-kids wds-cost-range=0 wds-default-cost=0 \
wps-mode=disabled
add disabled=no keepalive-frames=disabled mac-address=BA:69:F4:33:5E:B9 \
master-interface=wlan2-main multicast-buffering=disabled name=wlan2-guest \
security-profile=guest ssid=ap1-guest wds-cost-range=0 wds-default-cost=0 \
wps-mode=disabled
add keepalive-frames=disabled mac-address=BA:69:F4:33:5E:BB master-interface=\
wlan2-main multicast-buffering=disabled name=wlan2-iot security-profile=iot \
ssid=ap1-iot wds-cost-range=0 wds-default-cost=0 wps-mode=disabled
add disabled=no keepalive-frames=disabled mac-address=BA:69:F4:33:5E:BA \
master-interface=wlan2-main multicast-buffering=disabled name=wlan2-kids \
security-profile=kids ssid=ap1-kids wds-cost-range=0 wds-default-cost=0 \
wps-mode=disabled