I have since recently a problem with the top layer when printing with ASA (it also sometimes appears with PLA, but not to that extent). I dried the filament, did the calibration, and changed various settings recommended in other threads, like changing the infill type, but nothing seemed to have any effect. I first thought the nozzle touches the filament, but the defect is perpendicular to the layer lines. Any idea what might cause this?
Welcome to the community.
This is an example of under-extrusion. You will need to calibrate your filament. In this case, Flow rate calculation is off but if want best results, perform a complete calibration. You might refer to a recent topic on this where another member posted about something similar with the same remedy. Here is that post. Slicer or printer
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I did the calibration multiple times. This is a print where I stopped two layers before the end, and it looks fine. Shouldn’t this layer also be broken if it is under-extrusion? The defects really only appear in the top layer and are not with the layer lines but perpendicular to them.
Are you using ironing or something because that latest photo looks near perfect and I can hardly imagine how you end up with the original photos after two more layers unless its ironing with very little to no flow.
No, I am not using ironing or anything similar.
@Lenyo is right. Based on what you’ve shared, it doesn’t look like your filament was properly calibrated. You didn’t specify what you mean by “Calibration,” but if you’re relying solely on Bambu Studio for this, it’s not going to give you accurate results. If you followed the link I shared and used Orca, the calibration process can take over two hours, especially if your first attempt wasn’t satisfactory.
Even after calibration, specific models often need fine-tuning. In your case, I’d recommend looking closely at your upper layers—how many you have, and if they’re sufficient. A quick way to test this is to use a cube primitive model at about 2mm height to create a simple, repeatable test. Once you’ve got a solid test case, revisit the calibration process, adjust where needed, and get it dialed in. This will not only help with the current model but also allow you to use cheaper, non-Bambu filaments without sacrificing print quality.
Proper calibration is tedious but essential, and from what you’ve shown, there’s still some work needed to get the results you’re aiming for.
Humor: It would be at this point that my friend @johnfcooley will bring in his horse. 
“private joke intended”
In addition to what @Olias said, you should attach the .3mf so someone can have a look, something fishy here, might have to do with the dual coloring somehow.
Should be an honor getting one of these.
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