Upgrading Shepherd services

[Development of GNU Guix and the GNU System distribution.]

Hi,

I have a lot of custom Shepherd services.  Every so often I make a
mistake that stalls the step in 'guix deploy' that upgrades Shepherd
services, but without any error messages.

Unfortunately, I can also no longer run 'herd status', which likewise
hangs, or 'reboot'.  How may I debug such issues in my operating-system
declaration, please?

Kind regards
Felix