I did not need to close the run box but perhaps I needed to install the "Filter Handler Metadata Properties Extender," which I did on this computer.
The script saves the calculated sizes to the PDF itself, into the metadata custom field you configured with the manager. You can always use a PDF reader to check if the metadata got indeed saved to the file, e.g. File>Properties (CTRL+D) in Acrobat. The Windows File Explorer will use the PDF-ShellTools PDF Property Handler to access these properties, so these are available immediately after the metadata is saved to the PDF. That's why you didn't needed to close the script output window.
I don't think having the "Filter Handler Metadata Properties Extender" installed, or not, is related to the problem you experienced with the other script.
But, latest Windows 10 versions, e.g. 20H2, seems to have Windows Search issues, with the Search Indexer failing to index the metadata if, under the Windows Advanced Indexing Options, the PDF file type is set to index the properties and file contents, instead of just the properties. The indexer uses the registered PDF filter to gather the file contents and metadata properties (if also exported by the filter) and discard the metadata properties exported by the call to the properties handler, despite still calling it. This result in the Windows Search not finding by searching by any, supposedly, indexed metadata word(s). Having the "Filter Handler Metadata Properties Extender" registered fix this, as this filter also exports the PDFs metadata properties. When this issue is present, the PDF-ShellTools Reader Windows Search Explorer shows all the metadata columns empty.
Let's hope Microsoft fix this issue soon.
PS This is a great piece of software! I may even buy it! (I had thought that I would just be using it once but I am really liking it). When I rotate using PDF ShellTools it does not change the creator nor producer field of the document which is very good since my printer insists everything is made by Adobe or MS Word. Hopefully they will not notice.
Spread the word.