Well, I purchased some new cables from Amazon (12" straight) to try. Everything worked FLAWLESSLY today- no crashes, no lag... just made me love it all over again. Unfortunately, the cable I was using was also very new- maybe a month old.. I thought I was being slick- only 6", with a right angle on the micro USB side. Somehow I think manipulating the cable to plug it into the BT-300 must have strained it, although it looked like a heavy duty cable with a braided jacket. Hopefully this new version holds up better. Strange how finicky cables can be.
For anyone's reference, these are the new ones that seem to work well: https://www.amazon.com/gp/product/B01HGHV98G/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
This is the one that failed on me: https://www.amazon.com/gp/product/B01LX0IF95/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1