On the BeagleBoard.Org site in the "BeagleBoard.org Latest Firmware Images" section the "Debian 8.4 2016-05-13 4GB SD LXQT" image is listed as the recommended image. I propose that the 8.3 image be listed there instead because the wifi configuration by way of the suggested configuration method using connmanctl does not work for 8.4 and 8.5.
After testing from the sd card I flashed the 8.3 image to eMMC. It works. I can connect to my wifi. And it survives a reboot.
I also apt-get update and apt-get upgrade. connmanctl still working.