A few minutes ago I ordered new headphone cables, jacks etc. so I've
taken the opportunity to speak to a technician from Reichelt, since I
ordered the USB cable there, too. He doubts that the ferrite core dose
cause issues. His guess is a "Monatgsproduktion" (bad produced cable),
but actually removing the ferrite core solved the issues with the
PreSonus. Btw. I'll return the Presonus 1818 VSL. I already ordered a
Focusrite Scarlett 18i20 2nd Gen, less expensive at the moment
https://www.thomann.de/de/focusrite_scarlett_18i20_2nd_gen.htm . Maybe
it will work with Linux, as well as with an iPad.