You get it once per quest which doesnt really matter in this scenario
I know I used an sp3 from a previous fight on the path with a different champ but if the quest is counting that towards Sentinel’s special 3 then that’s an oversight or a bug
No that can't be it ..
Not even using a 6* Sent should count on that... Weird.
If you didn’t use a sp3 previously with Sentinel than maybe it’s your heavy. If you are parry stunning and then heavying to get to three bars he will drop some power to inflict a shock rather than reaching three bars.