Ok, I could reproduce it at least for one case:
The list in ```$RELEASE_PLUGIN_LIST``` is empty in case ```$SOURCESDIR``` (set to ```${HOME}"/.tmp/geany-plugins/"``` at the beginning of the script) exists but is an empty directory.
If it is not empty and includes a geany-plugins repository, then everything is fine. If it does not exist then it's created and the geany-plugins repository is cloned into it and then also everything works fine.
@dmaphy would need to tell if that was maybe what happened in his case.
If yes, the issue could be rated as an installation problem or unexpected environment and could therefore be closed as invalid. Or the check of ```$SOURCESDIR``` would need to be improved to check if it really includes a geany-plugins repository. But is it worth the hassle?