Hello Rene,
I seemed that all worked fine: Prompt for installation, Message for restart, etc.
I tested it with two other users with the same result.
I have imported the local update-site in our server update-site. Made the necessary updates in the extension.xml and created the document in our widget catalog. It still works without problem with version 1.02 and Notes 8.5, but not with 1.03. After that I made an installation from your local update-site via (german: Datei - Anwendungen - Installieren; to make sure I made no mistake with server update-site and widget catalog): Again not working, but also no error messages.
Kind regards
Wolfgang