Pi-Hole on Beaglebone Black

Missed this bit.
You could try figure out where that file "SoftAp0" comes from:

dpkg -S SoftAp0

sudo grep SoftAp0 -R /etc/

What is displayed when you run below 3:

sudo /usr/bin/pihole-FTL

strings /usr/bin/pihole-FTL | head -1

readlink /lib/ld-linux.so.3