To be more specific, If you have REST + DBX on your machine you might face this issue of inputs not showing up.
If you have this app installed , it causes all other Modular Inputs to not show up on the Manager->Data Inputs page
This could be an issue with the fact that when you upgraded to splunk 'X' version and have an app installed which is not supported in that version. You should uninstall this X version of app and restart Splunk to see inputs
I have the same issue on 6.5.2. You can access the REST inputs screen using:
The functionality of the input works perfectly fine.
Hope this helps.