On another router I've changed the base mounts to sync ie: mount /dev/md127 /boot -o remount,rw,noatime,sync before upgrading, but after a reboot it came back corrupted.

The configfile was complete before I started the upgrade.

Also on this one, booting back in the old version, removing the new version, re-adding the new version and rebooting fixed it.

Just tried to upgrade from April image and its failed with this error :(

The system currently has the following image(s) installed:

   1: 1.4-rolling-202307050317 (default boot)
   2: 1.4-rolling-202304050317 (running image)

EDIT: as roedie pointed out, a reinstall worked to actually get past this but got a migration error on firewall. It would not load at all with some python errors. I tried to manually load config but same thing. No possibility to proceed.

Is there any way to figure out what in the firewall config is broken?

I'm encountering similar issues on upgrade as well: the configuration fails to apply because of a broken config.boot file (incomplete; stops partway through, perhaps a migration issue?)

@blackhole at the Grub menu, if you have the image selected that you wish to boot to, hit e to edit the params for that entry and add vyos-debug and vyos-config-debug to the other parameters there to get more logging output on boot, which would presumably detail any config migration issues. Source: Relevant VyOS Docs link

A developer I work with reports this:

After nearly 30 reinstalls the upgrade finally blew up. The issue is in the initial copying of the config file, between lines 182 and 219 in the install script. That's where it happens... what's causing it / how it happens is still unclear...

So, with that commentary, I'm thinking @roedie that your filesystem suspicions are perhaps a thread worth following. (But I wouldn't know where to start diagnosing that.)