CCP Logibro today issued an advisory on capital manufacturing in Upwell Structures.
It seems that there was previously a bug where you could not install Capital ship build jobs in a structure that had a Supercap building module, but not a Capital one.
They have fixed this bug, but a new one has appeared.
If you have a structure with a Capital manufacturing service module in it, and you install (or have already installed) a Supercap manufacturing service module, and then unfit or offline your Capital manufacturing service module, it will cancel all your Capital jobs, even though the Supercap module allows for them to be built.
CCP have therefore advised anyone who has a Capital manufacturing service module on their structure to not offline it until this bug is fixed.
This seems to be a fairly niche bug, so would mostly affect people who are upgrading to a Supercap building structure setup, or who have both currently fitted, and are switching the Capital module out for say, a market module. However, the cost of lost capital building jobs can be quite significant, not just in ISK, but in time.
So, if you have a setup with Capital & Supercapital manufacturing service modules, or are thinking of switching your Cap module for a Supercap one, do not offline or remove your Cap manufacturing service module until CCP have fixed this bug.