Hi,
i read the instructions you’ve posted. Have you already tried this:
You should create a “download file” button and set it’s ID to “DLBtn”, for example. (Note: You have to enable the “ID” property in the bubble app’s settings. After that the “ID” field will appear in the object inspector as the last element.)
Next step: Create a text element “Download in progress…” for example. Set this text to Visibleonpageload=no. And now… I hope that you could switch to the text element’s Conditional Tab and create a new condition that set this text to visible if the FILEDOWNLOAD…PLUGIN’s.DOWNLOAD=active .

just an idea.

best,
jupxi