Sure, here is the translation of the text from German to English:
"Hi,"
@Wolfi_b: Exactly because the pulley in the middle has a slightly larger diameter, the belt should run in the middle. The belt only sees the gradient, not the absolute diameter

.
Based on what I see in the picture, the belt appears to have split lengthwise because a portion of it wasn't running on the pulley but was instead beside it. I strongly suspect that something is wrong with the pulley itself. Perhaps VAG-Tuning can shed some light on this.
Regards,
Sure, here is the translation of the text from German to English:
"Micha"