Plugin not loading when launching secondary window

[k-i-k-s]

Sorry I put this here since community website certificate is expired and is no longer accessible

I'm trying to create a plugin with the starter repo I cloned locally, I made some updates to have a custom build workflow with tsup, the desired architecture in Mailspring/packages/{plugin} is maintained of course (package.json pointing to lib/main.js and style in styles folder).

The plugin flawlessly loads everytime in the main window, but not always (or even rarely) when launching a secondary window, when creating a message for instance.
It's a bummer because I'm trying to add some functionality to the composer...

I tried to manually load the plugin with button Install a plugin, selecting my package (already present in the right packages folder), but it wipes data in every file then logging NoPackageJSONError, obviously.

Has anyone ever encountered such behavior ? I sure need some help here.

Thank you all in advance!