Can confirm this happening. Possible cause.
Logs from a 17 it happened on both pulls.
https://www.warcraftlogs.com/reports/B39fZbaPtXYygV68#fight=last&type=casts&start=14158935&end=14542589&hostility=1&source=29
He hits 100 energy and doesnt cast the spears, just straight into the firey focus. You can clearly see 5 events over 2 fights of firey focus but only 3 events of spears over the same fights.