We tested the whole calibration process of the sensors on a ProfiLux3 with firmware 6.19 and after upgrading the firmware to the latest version. It works, as it should.

Normally, the calibration process should not exceed five minutes (even with a tolerance level of one; you could use a higher tolerance and see, if it helps). There is most likely a sensor probe failure in your installation.
Double check the probes and the attached wires.