Assignments are core however ... "did process some plugin updates last week". Was one of those plugins for assignments?
There are assignment addons for submissions,feedbacks, even types.
Dashboard -> Site administration -> Plugins -> Plugins overview
and select additional plugins for a list.
Could be you've acquired an update to an assignment plugin that is affecting the core assignment.
Ghostscript path is an operating system thang ... and it's path is not normally changed.
Have ssh into server?
would return the path to the Ghostscript executable.
On a CentOS 7 server.
gs: /usr/bin/gs /usr/local/bin/gs /usr/share/man/man1/gs.1.gz
Translation ... the gs executable is found in /usr/bin/gs so the path in moodle would normally be (on CentOS 7) /usr/bin/gs.
If your Operating system is different or recently an update to gs has been acquired then paths may have changed.
In either/both cases, turning on debugging might provide some more specific information.