I'm using Toast 10 (v10.0.9) on a new iMac running Mac OS 10.11.6.. It is the latest update available as far as I can tell because the "About Toast 10 Titanium" Info box comes up blank.
When copying from one DVD to another using 'Disc copy' in Toast 10 the burn sticks at various stages midway through writing Track 1. On one occasion it stopped during disk verification.
There is no error message and mostly the only way forward is to force quit Toast. Even if the 'Cancel' button is not greyed out, selecting it does nothing. Also the DVD's icon disappears from the Desktop and details of the drive disappear from my "About this Mac" report.
Sometimes the DVD burns led continues flashing. At other times it stops flashing.
It is currently stuck writing track 1 at 69% with 4.09 minutes remaining to completion. I don't think the Mac going into sleep mode has anything to do with this.
The burner is an LG BPO6LU10 (ROM version HL03) Super multi Blue Blu-ray Disk Rewriter. The drive play movies back fine.