I would have suspected something like that if there was an hp utility to manage energy settings, but it actually is the standard "PC settings" win10 interface that affects this.
In the pc settings screen, "system" group, power options tab (see for example http://img.wonderhowto.com/img/original/00/31/63575955478586/0/635759554785860031.jpg
), the first item at the top rules on this: "SCREEN - on battery power turn off after XXX minutes".
If I change this value, when inactive the screen turn off after the specified time... and musicbee will mute accordingly. As soon as I move the mouse and the screen is back on, musicbee will resume playback.
Some news: I fiddled with this settings a little bit, discovering that the behaviour does NOT depend on electricity coming from batteries or the power line: I experienced it with battery power since the screen timeout was shorter, but it happens when plugged as well if the "plugged in" screen timeout is reached.
In this situation, I do not really know what kind of "less aggressive" power settings I could use, else than setting screen timeout to very long times both when on batteries as well as when plugged in. If you have any specifc hint on this please let me know!