I’m fairly sure the actual bomb prop has a lot of invis stuff on it which causes this, and you can see this when you drop it and it’ll hover or roll weirdly, my guess is that’s what’s causing it?
I've noticed this quite a lot.
You have to aim at a sort of 45-degree angle near the corner and it lets you place it, even then, you have to be near it to start the detonation.
This was actually due to a 5 second cool-down every time you missed, making it appear like you "missed" when you would try to click again when aiming in the correct position. I have fixed this.