HA fail - Passive node not accessible and HA not working

Hi All.

Was checking firewall prior to firmware uprade and discovered my HA pair is operating properly.  Ran into some more issues and am hoping you guys will be able to help me unpick it all.

When I go to System Services>High Availability:

1. The "Serial Number" has a red "Standalone" next to it

2. The "Peer Serial Number" has a red "Faulty" next to it

I've looked through section #7 in this very useful help doc: https://community.sophos.com/products/xg-firewall/f/sophos-xg-firewall-general-discussion/79041/troubleshooting-guide-for-xg

and can't see any issues.

WAN is not DHCP or PPPoE

Can't get to passive device to check whether HA is disabled or not

DMZ_HA port has been created and SSH is enabled

I'm not using a crossover cable, I'm using a normal CAT5 cable to link the 2 devices together but that is OK from what I have read

I've run show details for HA on the console of the Active unit and it looks like this

But I can't ping 192.168.50.6

I've run out of places to look to find an error.

Thanks

Jon