I'm using 2020 SP1 now and meet the a similar problem. The project was able to be built well until I turned one sub vi to inline. Then the error 1052 is always there.
As mentioned, I can build the project again after I deselect the 'Modify project ...' option. A strange thing is after that, even I turned the sub vi back to allow debugging, it still has the build error with 'Modify project ...' selected. Have to uncheck this option finally.
