@jn6091 When plugin signed it creates MANIFEST file with all included files and their properties. If any of the files modified, it will be skipped and plugin should be resigned.
If you enable the Dev mode, MANIFEST file should be deleted. It was recently updated in the documentation.
If you do the provided steps in the correct order, plugin should be loaded successfully.
You can take a look at our Panel template for example: GitHub - VolkovLabs/volkovlabs-abc-panel: Template to create a new @grafana panel plugin.