It’s becoming the norm that tech crew are unwilling to Start the APU until the final moment.
untill the APU has started the ground crew shouldn’t remove the external power.
my observations are that tech crew get clearance APU just started or about to start.
Ground power is removed sometimes to early. Complete reboot needed which takes 30 to 40 mins aircraft dependent.
Some tech crew English is appalling, some refuse to speak in English, mixed messages happen causing last minute snags.
Do not always blame the contractor. In my experience most of the time the fault is with the tech crew. Lack of communication then want immediate pushback.