Hey I figured it out after several months - whatever Apple did in their OS, it seems to related to power of the BD writer. Just fYI I'm on TS02 for my Toshiba-Samsung Storage Tech (TSST) SE-506CB Blueray writer, Imac 2015 on high sierra. I have it connected to an Anker USB 3.0 *powered* port - if you have a USB hub /w the powered port put it on there. After that I've been able to write DVD's. I used to always get this unrecognized command, and the BD writer would reset itself.. I figured if it reset, it was probably power draw related.
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