I finally caught a slave ‘stalling’ in the act!
0: INFO: Lightning: Checking render elements
Scheduler Thread - Render Thread 0's task filename "\\sfs-file\repository5\jobs\000_050_000_0725f500\tasks\000_050_000_0725f500_00001_1-1.Rendering.Daedalus" could not be found
Scheduler Thread - The task folder contains the correct number of tasks, which would mean the task had been requeued
This happens on any job with black frames that render in less than a second or two. So I’ll end up with a bunch of tasks the next morning which have finished but are still listed as “Rendering” and at 0%.