Just an update:
For those experiencing NAT hairpin/loopback issues, please try the following commands via SSH into the router to see whether they resolve the problem:
sysctl -w net.bridge.bridge-nf-call-iptables=0
sysctl -w net.bridge.bridge-nf-call-ip6tables=0
If this resolves the issue, you can make the change persistent with:
echo "net.bridge.bridge-nf-call-iptables=0
net.bridge.bridge-nf-call-ip6tables=0" >> /etc/sysctl.conf
reboot
Please note that if you adjust the network acceleration mode again (disable / software acceleration, then hardware acceleration), you will need to rerun the command to fix it.