First layer noa always perfect

My printer is calibrated, but I have troubles with first layer. Before every print I do auto bed leveling and sometimes the first layer is perfect sometimes the first layer is not perfect. Anny suggestions what can be wrong?

There are so many reasons.
The quality of the filament, the temperature settings (nozzle and bed), the printing speed of the first layers and so on.
Unfortunately it’s not just leveling.
Calibration prints should be made beforehand in order to gradually fix all the settings, not only of the printer but also for the filament.

Yes, but this happen with the same filament and same settings…

Have you made previously those calibrations ?

yes, i made previously those calibrations