Diverter valve errors, APR tune

Yesterday my Golf 1.8t threw up an EPC warning light. I took the car to the dealer and they ran a scan, which showed an intermittent diverter valve error. They cleared the code and sent me on my way. Almost immediately it happened again, and this time the car went into limp mode. I limped back to the dealer and left it with them for more diagnosis.
Two questions: 1) how likely is it that the dealer will blame the error on the APR tune? and 2) how would you suggest I argue against that assignation of blame?
Thanks in advance.

It depends a lot on the dealer. There's a chance they will completely blow you off, in which case the diverter valve is not too expensive and super easy to replace. Obviously an APR tune won't break a diverter valve, but some dealerships are super weary and won't even touch modded cars. At my local dealership I would expect them to potentially even ignore the fact that I don't even have a stock turbo if I was trying to fix the problem you are having, they are really good.

If they do send it back your way I wouldn't bother fighting them on such an easy fix, you might even be able to find a used diverter valve for very cheap here on the forums. Then it's literally right on the very top of your engine bay, 3 allen bolts and you're done.

EDIT: Worst case scenario: https://www.shopdap.com/06h-145-710-c.html

Thanks for this reply. I think if it come to this I will probably replace the DV in their parking lot out of principle.