OK I have resolved my issue by starting from scratch and re-installing everything.
My issue appears to be caused by the old OS I was running – Angstrom – which is what the BeagleBone originally came with back in 2014.
I flashed the latest Debian image to the eMMC with image “bone-eMMC-flasher-debian-10.3-iot-armhf-2020-04-06-4gb.img.xz” – downloaded from https://beagleboard.org/latest-images
I found instructions here useful for performing subsequent updates and disabling unneeded services – https://www.selectiveintellect.net/blog/2021/8/15/setting-up-a-beaglebone-black-with-debian-buster-for-iot
I then installed the Unified Firmware with these instructions – https://openthings.freshdesk.com/support/solutions/articles/5000631599-installing-and-updating-the-unified-firmware
Works now 🙂