There is no drum sound when re-opening the project.

That might be a misunderstanding about the free version of the plugin. The free version has no sound until you click the SKIP button in the bottom right of the plugin window. So you have to open the plugin window once at the beginning of every session, even if the plugin has already been added to the project.

After skipping the start screen there are no limitations.

By buying a key i.e. donating you can disable this start screen permanently and get instant sound at the beginning of your session. That is entirely optional though.

Donate here and get a key