On each new print using the Original Prusa MINI printer, the first layer calibration is printing at a different Z-offset than previous set. The value is the same, but the actual distance of the nozzle to the heated bed has changed. The first layer is now too high above the bed, or too low.
The MINDA sensor for the Prusa MINI is heat-sensitive and may even be defective. The sensor may need to be replaced.
Ensure that the sensor is not functioning properly:
- Ensure the sensor is a credit card width from the bed when the nozzle is placed on the bed. Test the next print.
- Ensure the firmware is up to date, and test the next print.
- Do a factory reset of the printer, and test the next print.
- Run a first layer calibration again, and test the next print.
If none of those seem to resolve the issue, replace the MINDA sensor. Contact Prusa Support to let them know that the sensor is malfunctioning, and provide the troubleshooting steps you have already taken.