LabVIEW's option to Replace with subVI contents is grayed out and I can't click in it. I've seen this happen when my subVI has an indicator inside a structure in the subVI.
Take out all indicators in your subVI from any structure (while loop, for loop, sequence structure, disable structure, case structure, etc).
This is a feature introduced in LabVIEW 2017, and it's documented under the software readme file: LabVIEW 2017 Readme for Windows
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