I have an LG External Blu Ray Burner attached to my 27" iMac running El Capitan 10.11.6 with a USB 3 chord.
I tried to burn a DVD today and it would not work. I opened Toast and it said "No Recorder Found." I closed Toast and put the DVD in and it did not mount on the Mac desktop.
I open up Toast and it recognizes it. I then start to burn the disc, but it does not start to burn I cancel the operation and then Toast does not recognize it anymore.
I close Toast and re-open it. I does not recognize it again.
I close toast and put the disc in and it mounts on the desktop as 'Untitled Disc" I put the files in that disc and the "burn" button is grayed out. I cannot burn the disc. A few seconds later 3 or 4 "Untitled Discs" appear on the desktop I have to move them to trash.
What do you think is happening? Could it be a bad USB 3 wire or a bad plug that came with the DVD Burner?
You don't mention if the player is new, old or what. Has it ever worked right? Was it working before you upgraded to El Capitan? If so, did you update the version of Toast for 10.11.6 if an update exists?
I had a similar problem, and the burner was going bad. I borrowed a second player and found it worked fine. Bought a new player. Haven't had a problem since. Random drops like you describe are not usually a cable. It normally works or not.