I’ve noticed this before, did they change either the Longshot base damage or the Health of the Elite Grenadiers?
Some of of them need a 2nd Longshot bullet to the head after losing their helmet so 3 bullets in total. Some of them only need 1 more after losing their helmet.
Range doesn’t seem to be a deciding factor, I can shove it right in their faces and they still survive it, same on long range - some survive, others don’t.
These are also the only enemies where I saw it happen.