The ASUS is direct attached and the Pioneer is USB. Optical drive 'BD-RE PIONEER BD-RW BDR-XD05 1.20d' opened in OS access mode. Optical drive 'BD-RE ASUS BW-16D1HT 3.01d' opened in OS access mode.
I am now at macOS High Sierra 10.13.6 (17G11023) (High Sierra) and firmware was upgraded to 1.39f11 and suddenly all Blu-ray discs stopped mounting. I updated to High Sierra recently (to keep getting security updates) on my 2010 5,1 Mac Pro and with the update came a firmware update. I am not sure if anyone else has seen this, but it is utterly confounding.
