I updated to 4.8.4 from 4.8.3 thru the ui, and now clicking the app link for the default page from the sidebar or the Apps page returns:
404 Not Found
Return to Splunk home page
Page not found!
View more information about your request (request ID = 5ab384019a7f429c6a1150) in Search
Is this the "invisible apps" error from two years ago?
Splunk 6.6.3 on Linux
Can you try configuring it with cli:
already verified inputs.conf are the same on the Splunk server and the forwarder on the Windows machine.