The problem is solved and not related to the MusicBee, but very strange and unbeliveable.
I have an album and from that I use only one track in my playlist. The track was too loud. I reduced the volume in the playlist (right click on the track, edit..., settings tab -> volume adjustment - 35% and after I set up a custom equalizer to boost the bass). After when I finished it was everything perfect for me. But today I played the playlist and that music is almost silence, the sound is very very very low, other songs from other albums are good same like they were. I opened that silent mp3 in two different player (winamp, mediaplayer) and the sound level is same very very low. I opened other tracks from that folder (same album) and another tracks are similar, almost silent.
First I set off the Replay gain, nothing changed, from the settings tab I set back the volume in the original, nothing happened. I restored the volume to original form the menu, nothing. ;( I was almost crying.
I opened the file in music editor, I see the waves of the music, it seems like the waves are there, but I cannot set back the original volume.
Another try: Set back the original volume, and after Analyse volume menu and Adjust calculated replaygain values I set to zero and Proceed, after in the Track gain information shows -7,3 dB.
I removed the Music Bee and nothing changed the mp3s in that folder permanently almost silent tracks. Reinstalled the music bee nothing changed.
I would like to ask help how can I set back the track files to play on normal volume? Or is this remain permanent and I have to convert my CD again? Thanks a lot, I am looking forward for a solution, thank you very much.