Base lacquer becomes rough/ flaky/ matt

Hello guys, first of all sorry, if this has been treated maybe already 100x, but I just just stand on the hose, don’t come any further, and find nothing… Here’s my background: I have often painted small parts (door handles, mirror caps, etc.) by can, and the result has always been quite good. A few weeks ago I painted a bumper for the first time. Also got good. At my mother’s moose repaired a tear damage, spatulas (that was my first attempt) i not so good, but then painted, sanded, polished. Also good. Now I’m trying to paint a fender, and it doesn’t want to be anything (work like a hobby, i.e. with spray cans): Performed work: – fenders of course came to shredded, so with 400s the scars largely out, then 1200er, then 2000er (everything wet) sanded. – cleaned and degreased. – fenders made completely with rust protection primer – the upper half of the Koti with fillp Rimer made (there were all the scratches) – all sanded again with 1200er and 2000er – again cleaned and degreased – base varnish (1K) not covering over – maintained – base varnish covering – base varnish matt and rough and you can see the traces of the sprays (spotty) – again 1200er and 2000er – again base varnish, again matt and rough and flecky. – again 1200er and 2000er – Ne wide jet nozzle on the can -> spewed like sow. Mist. – again completely sanded from 400 – 2000. – Again normal nozzle on it. Again bad result. Spray distance: ~ 25cm, short spray runs with beginning and end outside of the workpiece Manufacturer Color: Multona (I have always used a new can has the same result so far) Manufacturer Clear varnish (as soon as the base varnish becomes possible): SprayMax (2K) Manufacturer Spray filler: SprayMax Paint place: In the carport in the shade (there are almost 0 particles & Viecher flying around – so far max. 1 inclusion with everything I have painted there) What the hell is different about the fender, like the X other things I’ve painted so far?! What am I doing wrong? I stand here like the ox in front of the mountain and don’t understand the world anymore About a tip or help I would be really grateful! Greeting, Alex