Sentinel shooting at wall
The sentinel tends to shoot directly to the closest corruptron even if it implies that the sentinel projectile ends in a wall and the corruptron remains unharmed.
Archers have the exact same issue. The aiming/hitbox on arrows is much too precise to be incredibly useful. This causes a lot of situations where two archers next to each other cannot hit the same target, only one of them can hit the one directly below the other.
This is discussed with images
I cannot say if it is the same bug as I have no arrow to show the direction of the shots. Currently, a red explosion happens on the sentinel and that is all.
The situation is this one:
My sentinels are on a very high spot (higher than what the screenshot shows) on small balconies around the tower, shooting at corruptrons either under them or inside the tower where they have dug.
So perhaps it is the same bug, but downward.
It may also be that the sentinels shoot at corruptrons they cannot see inside the tower.
I have the save file, but it is laggy as there are fifteen waves of unkilled corruptrons on the ground floor. :-)