Hello Timo,
thank you so much for your response! I played around with the model and I seem to have fixed the problem. Maybe someone who stumbles across this forum has the same problem, so I can say what I did:
1) I made sure that every measurement model / every factor had one loading fixed to 1.
2) I made sure that every latent variable has a residual (this is what caused this particular problem).
3) I also made sure, if I made a model formative (the arrows point from the manifest variables to the latent variable, not vice versa) that I deleted the residuals on the manifest variables.
Thank you again for your work and I hope this can help someone who’s also new in SEM!
Cheers,
Rayne