Hi Keith,
Just a word of caution on how Home Assistant runs shell commands. You use shell_command platform in your yaml, I have a bad experience with command_line one.
Depending on the way you invoke the Home Assistant, the shell commands can be executed with either bash or sh. The last one is severely limited, of course, and often leads to errors and problems.
I discovered this with my tiny CPUtemperature script that worked fine until I … implemented the systemd startup script. See the screenshot:
I documented this behavior in the original thread Autostart using systemd and I’m still trying to troubleshoot it further.
Similar phenomena could contribute to the problem described here.