Thank you all for your replies!
I have managed to identify the problem and it is not related to a BMS bug after all.
After the fresh installation I did yesterday, I found out that in addition to the previous ones, now I also lost “Engine external” and “sound effects” sounds at all…
So, after several things I tried, I also tried to redirect the output sound from my 5.1 speakers to a different device (headset). And guest what? all sound could be heard…
So, the problem was that different type of sounds are going to different sound channels (i.e Cockpit sounds goes to front speakers while RWR sounds goes to central speaker) and due to a button pressed in my 5.1 speakers, output was downgraded to stereo instead of 5.1. However, this did not work for BMS. And as it seems, in the two installations tried, different type of sounds were affected each time. Note that in Falcon AF and Falcon 4.0, nothing similar was happening. At both these installations, all sounds were going to front speakers, as stereo.
When I configure again my speakers to 5.1 setting, all sounds came back also in these speakers.
Thanks all of you again for your ideas and proposals.