Cannot upgrade to enhanced metadata

Alright, I think I figured it out.  It seems there's definitely a bug in PowerBi when it tries to auto-convert to the new metadata format.  The issue is indeed with special characters in the Transform File functions.  To fix this issue, I did the following:

• Open the impacted .pbix file
• Go to Transform Data
• Locate your query which calls the "Transform File" function
  • Find the steps in the query which specifically call the transform file function
    • For me, these steps were "Invoke Custom Fuction1" and all steps which referenced the "Invoke Custom Function1" step
• Rename the file path part of the function name to something without special characters
  • In my case, the before and after code for this step are below replace <server name> with anything you want without special characters:
    • BEFORE:  = Table.AddColumn(#"Filtered Hidden Files1", "Transform File from \\<server name>\<path>", each #"Transform File from \\<server name>\<path>"([Content]))
    • AFTER:  = Table.AddColumn(#"Filtered Hidden Files1", "Transform File from <server name>", each #"Transform File from <server name>"([Content]))
• Now you need to go up to the "Transform File" function and make the same changes there anywhere the old function name is referenced - from the function name to steps within the function itself.

This was a total pain to do once, let alone the 20 more times i'll have to do it in various reports, but for me, this resolved the issue and I can now refresh my data from within PBI Desktop.