Question about MAXIFY GX7050 - 657198

I have just installed a GX7050. Everything works so far. However, the printer smears the pages facing forwards when duplex printing. The printout shows the text image and a shadow of the same text offset approx. 2cm downwards. This looks like a problem that occurs when refeeding. The same thing happens with more pages - always only on the side facing forwards - but the soiling is slightly heavier. I have set the printer to duplex printing by default. These are the first pages I ever print. What can I do to stop this problem?