I often create backups when the PC is, as far as I know, idle with a browser minimized. Until recently the browser has always been Firefox. I recently started experimenting with Chrome. It seems that many, but not all, times PhyLock can 't lock volumes. I have a large timeout (60 minutes). In most cases PhyLock just waits until that time expires unless I do something. It also appears that simply closing Chrome causes the backup to start promptly.
This is just for information. I'm not expecting anybody to know why this happens.