This is related to https://github.com/metabrainz/picard-plugins/issues/64.
At the moment, the plugins API lists plugin versions that are not compatible with the version of Picard calling the API/most recent released version of Picard.
This should be fixed by either
- not listing plugins incompatible with the most recent released version in the API and/or
- having different lists and API endpoints for stable and unstable versions and/or
- having Picard send a list of supported PLUGIN_API_VERSIONS along and dynamically building the plugin list based on that