already tried to group audio, video etc.?

Quote Hello,
I made a film with transitions (fade). This film contains several music.
I would like to remove some transitions (fade). But when I do, the clips that follow "move" and the music is no longer synchronized...
How can I remove a transition without making the other clips move?

Sounds like you may be using overlap transitions, so when removed, this overlapped section adjusts and moves all the timeline content.

If that's the case, you essentially need to trim that overlapped section so nothing else moves. One way to do that is the following:
1) move timeline scrubber to left side of transition
2) select left clip and split
3) move timeline scrubber to right side of transition
4) select right clip and split
5) select this transition section and use Shift+Del to remove fade transition and video while not moving anything on the timeline
6) you now have the right clip in this old overlap transition region, one can adjust to be left clip, right clip or parts of either or reverse above steps and you'd have left clip in this old overlap section

Jeff