ReadyNAS Backup does not start using backup button

Hey community, 

we often face the issue where readynas backup job to external usb drive  isn't started properly when pressing the backup button.

There is 1 backup job configured, which can be launched using the backup button. 

1. We connect the disk, 

2. Wait few seconds,

3. Press the backup button, 

in 5 out of 10 cases it's going well, backup launches and completes successful, but in 5 cases nothing happens after pressing the backup button. 

The worst scenario is when you just disconnect the drive in this state. Then it's getting write protected since it's not disconnected properly (which usually happens at the end of the backup job). After reconnecting the write protected drive and retrying the backup you get the backup error "cannot access the target..."

We face the issue for years now. Is there anybody having the same issue or any ideas?

Problem is not related to the external hard disks - seen the same issue with various drives.

Thanks guys!

Cheers,

Flory