Answer
In a confirmed case with no other identifiable cause, applying pending Windows updates and rebooting the relevant servers (application/print infrastructure) resolved this kind of unexplained print-processing slowdown. There wasn't a clear root-cause diagnosis beyond that, so if you hit a similar sudden, unexplained slowdown in Crystal-heavy print processing with no configuration changes to point to, checking for and applying overdue OS-level updates followed by a full server reboot is worth trying as a general troubleshooting step.