The plugin does not work when it is installed by Composer at the project level.

[herewithme]

Composer autoload try to load:
"autoload": { "files": ["handler.php"] }

from : julien731/wp-dismissible-notices-handler
at the global project.

This file handler.php generate a die() because it's loaded before WP.

[MaximeCulea]

I think I could have a look and change plugin's vendor-dir.
To be continued ...