Acronis TI 2021 runs backup at wrong time

Hi,

I have two Windows 10 Computers scheduled to backup on a NAS-drive after office hours mondays to fridays at 6.30 pm and power off computers after backup. It happens sometimes that backup doesn't work and the computers (both, but not both at the same time) are running the next morning and finish the backup at 8.00 am. I have checked the power saving settings, switching to energy saving mode is switched off. I have two error reports at Nov 11th, saying 'Locking of file failed'. From then backups worked with the problems mentioned above. Has anybody a suggestion for a solution?

Achim