Problem with printing

Where this problem can come from? I have no way to control the situation.

Looks like underextrusion, maybe in combination with a direction change or support member location. Possible causes would include walls set to be too thin, not enough infill to support the slanted wall, or insufficient plastic flow (from partial clog, bad e-steps, or printing with too fast a movement speed).

This is underextrusion.
If you did not already, calibrate your E-Steps/Extruder. See here: Extruder Calibration a must
If you did, my second guess would be that you have some oozing from the nozzle while it travels, losing pressure. Thats rather normal. To compensate, use extra prime amount after retraction/travel. That should help. See e.g. here: What Is Retraction Extra Prime Amount in Cura? (Detailed) - 3D Print Beast

ElloryJaye and Hauke’s suggestions are the best places to start. Once you’ve eliminated those issues, I’ve had a similar result from filament binding during certain movements. If you don’t have a filament guide or alternate spooler holder, I suggest you get one or the other (after going through the above recommendations).

Here is another example of a printing problem. Basic, first layer. And this is not the first time. It seems that this is a bug in the file when translating from file STL to printer.

I don’t think it’s underextrusion, as I just calibrated mine and still see the issue. I think it has more to do with the start/end at a wall seam. And it is most visible in circles or shapes with >90° corners. Right angle corners seem to hide the issue better. I’ve also used Cura’s seam setting, set to random, and that helps reduce the issue.