OK I re-installed from scratch and then updated excluding the kernel and mkinitcpio:
$this->bbcode_second_pass_code('', '
pacman -Syu --ignore linux-aarch64 --ignore linux-api-headers --ignore mkinitcpio
')
After the update I checked the system was not doing anything crazy and rebooted - it did reboot and it did allow ssh in!
So now everything is running and the only remaining updates are the kernel and mkinitcpio:
$this->bbcode_second_pass_code('', '
[root@alarm ~]# checkupdates
linux-aarch64 4.16.6-1 -> 5.7.2-2
linux-api-headers 4.16.1-1 -> 5.6.11-1
mkinitcpio 24-2 -> 27-3
')
So the problem is either with the 5.7.2 kernel or mkinitcpio but at least the system does run and I can run diagnostics. However hopefully something can be tested to see where the problem lies and also hopefully a kernel update will resolve the issue. I have a standard rock64 so I am amazed that I seem to be the only one who has seen this issue.