All my Zigbee devices stopped working today too. I’m using the Digi XStick. I had previously managed to get them working again in 0.12 by following the steps in this post, including re-installing the Zigbee add-on.
But now the following error was surfaced as a toast in the UI:
Failed to start add-on Zigbee: /lib/arm-linux-gnueabihf/libc.so.6: version 'GLIBC_2.28' not found (required by /home/pi/.mozilla-iot/addons/zigbee-adapter/node_modules/@serialport/bindings/build/Release/bindings.node)
Neither a reboot nor re-installing the add-on seemed to help.
Currently sitting in the dark 
.