Most likely the Argo Therm must have no, or not enough compressed air. Compressed air is needed to cool down faster.
The Argo Therm is capable of sintering perfect results, even without compressed air, but then, due to the longer cycle, more argon is used. (Truly twice as much)
Make sure that your compressor is powerful enough to supply all the connected devices. Eventually your current overheated (and thereby stopped) during overnight sinterization, but cooled down again and seemed fine in the morning as you have returned to the laboratory.
See attached PDF for the Ceramill Argotherm Dos and Donts