Planted grenade won't activate

I plant granade and when the enemy goes through it, it just won’t explode. I’ve lost Act 1 Chapter 4 Insane two times because of this.

I’ve noticed this on my first playthrough on Intermediate, but i’ve always planted it like the Scout’s mines - in the vicinity of the enemies. So i thought, it needs to be triggered by an enemy outside of the grenade cone, who will eventually go inside the blast radius during their turn. So i did this on my Insane playthgough and it worked until this mission (Act1 Chapter 4).

During this mission it didn’t blow up on two occasions. First, i’ve planted the mine with Sid during 85% enemy reinforcements just after the checkpiont, where the enemies spawned, So i restarted.

I really didn’t remember how the next waves spawned so i was lurking the first one to one side of the map, just to get spawned with a wave 2 or 3 times bigger than the first one (playing on Jacked for the first time it was a nasty surprise). I was like: NO WAY. I’LL RESTART. But i saving-quitted and got back to see if i could turn the cards. Well … i did …

I had to sacrifice 2 characters to save Sid and Gabe and i was in a very good position to finish the Chapter with 8 enemy reinforcements left, just to not let another planted grenade triggered and getting a shotgun in my face from a 25% health Grenadier (who should have beend killed by that planted grenade).

So … with this experience i decided to find the first GT official forum and get into it, because Goggole doesn’t seems to give a f*ck.

I’m completely OK with restarting a level because of my fault (i already did in Chapter 3), but when the game decides to get in the way … well that’s another story you know?

And what about the Ironman?

I mean … i love this game so much, that i went back from XCOM. I was at the end of Act2 and found it really repetitive. So i started to play XCOM for my first time and i went back to suck it up and finish this game instead. It took me 88 hours to finish it, just because i like the customisation side (it took maybe more than a half of the time TBH).

Now i just need advice about the grenades planting ability, as that makes my playthrough reallly not worthwhile.

Thanks in advance!