Thank you very much for the answers!
So I probably don't need to worry about the flashing screen and sound? It does concern me, but I haven't had any other problems with the software.
I finally had som time to try out these methods at least.
So, I changed the temperature to 230 C, did some atomic nozzle cleaning and ran the flow test you provided, Torgeir. I didn't understand what cover to remove to observe the stepper motor though, but I didn't notice any immediate strange movement duing the print.
At 9mm/s the plastic starts to get very thin, a bit transparent, and at 10 mm/s it's held together by hopes and dreams in some places. It's better than I expected though, and I didn't hear any grinding/skipping back from the feeder duing the entire print. It did grind when I switched the material after the atomic method though.
What should I take from the result?
Just for the sake of trying I made a small, more advanced print with support structure and retractions. The quality is actually worse than before, I assume because of the higher temperature, but there was no feeder skipping at least.
It seems to be very inconsistent in what amount of material it extrudes, it's either too much and gets zits/stringing or these thin sections with small holes, mostly on the support structure.
For the print(s) that failed earlier the print speed was 60 mm/s, layer height 0.1 and nozzle 0.4, so the volumetric would be 2,4 mm^3/s? It seems quite low.
I didn't change the retraction for this print, it's set at 4.5 mm in length and 25 mm/s in speed on the printer itself, in Cura it's enabled but the boxes for retraction length/distance are greyed out for some reason? Should I try to go even lower than the 4.5 mm in retraction?
I forgot to loosen the screws on the feeder before the flow test print, but did it afterwards and a couple of them we're really tight so hopefully it did something good.
Thanks again for the help, it's tricky to find the problem with all these factors playing in! You think you're starting to understand something, then you find ten more things to consider.