Strategies for improving the reliability of Flex Pitch

I'm pretty new to using the Flex Pitch feature, since I rarely record vocals. I can get it to work okay, but I'm having trouble getting Logic Pro to reliably enable the feature. Sometimes one audio region on a Flex Pitch-enabled track will allow pitch correction while other audio regions on the same track that are also Flex Pitch-enabled won't.

I've heard that sometimes switching from Flex Pitch to e.g. Flex Time, or pasting the region into a new track, will enable pitch correction. But even these strategies seem sort of guess-and-hope. Are there any other strategies, either during initial tracking or later in the process, that can improve the reliability, i.e. the simple availability, of pitch correction using Flex Pitch? If I can get it enabled on a track, I can get it to work. It's getting it enabled in the first place that's the problem.