I've done the initial mission through Skylar and have destroyed one other rail bridge (currently on 2/4)

But I am having trouble with the two rail bridges on the Champagne-Ardenne/Lorraine border where I can place 3 out of the 4 charges but cannot place the 4th correctly

There is no flashing decal to place (the yellow marker is there, however)

It seems to be the same section of the bridge as no matter which order I try to place it in, the certain section won't place or show the flashing decal

Does anyone know a way around this? The perk is great

Make sure you have enough Bridge Killers. They're consumables like dynamite, and sold by the same guy.

You can only carry a max of 10 so you'll have to refill eventually as each bridge takes 5 charges. I was stuck for the longest time as well thinking it was a bug.

Additionally, I noticed a little bug when placing the fifth charge on the top of the bridge, on the tracks.
If your weapons are holstered, you may be unable to place the final charge.
Taking out a weapon (such as a pistol) or dynamite fixed the issue for me.