The open door prompt has been glitchy since ARMA2, this is particularly evident with large outdoors gates such as the ones in the Elektro power plant, the player is required to hold his reticle steady over specific parts of the gate otherwise the prompt won't show up, what's worse is that the prompt seems dependent on the same factors which apply to weapon aiming and steadiness so that when you try to open a gate if your character isn't steady (i.e you just ran for a bit) your reticle will keep moving around making it difficult to aim it at one of the bars and getting the gate to open.

This of course makes opening those gates unnecessarily difficult and puts the player into a risky situation where he has to strafe and move his reticle looking for the magic spot which will bring up the wanted prompt, with the reticle moving about making this all the more difficult.