Problem with cutter and stamp

If I print cutter and stamp together, this is the result on the cutter. If I print individually, it doesn’t happen. Why?
Immagine 2022-05-20 222133

The issue itself appears to be one where the hotend cannot maintain pressure and so after travel it takes some time before pressure is reestablished, during that time there is under extrusion. The cause can be a clog, or bowden gap.

As to why it only happens when you print both at once - two things I can think of - one is that it will print faster, when printing fewer things the slicer will typically slow the print down to give each layer time to cool. The second, is an increase in travel distance when there are two items being printed.