It was a reed quintet piece before (ob, cl, sax, bsn, bcl) and maybe before that that concert band piece (hence the trombones maybe). I deleted all the reed quintet instruments and created 4 new bass clarinet players. I indeed also noticed that the filesize is unusually large.
The thing is: I already created a completely new project and imported the master page templates. But then I have to change al the custom font settings and margin settings I use in my projects. But, maybe that’s the best thing to do right now 