ECM bug on burner mission?

I have done the hawk burner mission dozens of time with a double ECM (Gravimetric for caldari ships), but this last time, it was somehow litterally impossible to jam the support Bantam ships. With double ECM active on a single bantam, I would get maybe one jam cycle every 10 ECM cycles. I thought at first I might just be extremelly unlucky but It remained like this for about 10 minutes.

Usually i would get one every two cycles or so at least. The chances of this happening seems statistically impossible.

Is there a bug with the ECM module not working on some instance of NPCs ? could it be possible that NPCs soemtime get randomly assigned insane sensor strength ?