'ADFS won't show additional HTML file

I'm running an ADFS farm on Windows Server 2016. The service has an active theme named "OwnCustom". I added a small HTML file to the theme with the following:

Set-AdfsWebTheme -TargetName OwnCustom -AdditionalFileResource @{uri="/adfs/portal/script/note.html";path="c:\temp\note.html"}

Expanding the theme content with ...

Get-AdfsWebTheme -Name OwnCustom | Select-Object -ExpandProperty AdditionalFileResources

... shows the file is there. However, I'm not able to access the file via browser, instead I'm taken to an empty page as if the file wouldn't exist at all.

ADFS Sign-in page won't load custom font indicated a similar case where it was confirmed by Microsoft that hosting font files this way is not supported / does not work. However this answer was specific to font files and the workaround was to use a different extension so I'm not sure this would apply to .html files as well. Other than that there's not many ways I can figure how to troubleshoot the issue.



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