I had a private property named _rxQuotedUnitSearch, left the default blank.
It's initialized in the constructor, but I was getting the warning, "private property _rxQuotedUnitSearch is never used". This prompted me to realize I meant it to be protected rather than private. Changing it to protected, I was still seeing the "private property" warning. Told Analyser to do its thing, and the warning went away.
It is possible this warning would have gone away if I ran Analyser before changing the access modifier. The sequence was that I created the property, then referenced it in the constructor code. So for a few seconds, the warning would have been valid.
I assume this is some kind of update bug, but if one does in fact have to Analyse, Run or Build to force warnings and error messages to be re-evaluated, that's an expectation that should be set in the docs.