For communication, always make sure you use the correct radio and the corresponding PTT button. Also, making sure that the ATC belongs to the same coalition as you doesn't hurt.
Then, if you can contact ATC, make sure you use the ILS of the RWY that they tell you or if you have the possibility, force a certain runway to be active by adding some wind, preferably something like 5m/s / 10kts as it seems lower speeds may cause issues / irregularities.
Also keep in mind that some ILS can be bugged (Al Dhafra is an example I believe) and god knows how the extremely limited ATC of DCS is handling airports with more than 1 seperate runway.