Hmm the error is docker reference format, which suggests that there is an issue with one of the parameters. Did you change any of the addon settings? If so, go back to default and try again.
If not, it could be an issue with coreelec. I suspect the way I determine the arch is no longer working. They probably renamed it.
Here's my logic to determine whether it's x86_64 or arm: "sed -e '/LIBREELEC_ARCH/ !d' -e 's/[^.]*\.\([^"]*\).*/\1/' /etc/os-release"
If they renamed it to COREELEC_ARCH that would surely break it.
Can you do "cat /etc/os-release" and post the output?
Thanks