When Flex is enabled for a track, the Flex & Follow pop-up menu is available in the Use Smart Tempo with multitrack audio files in Logic Pro is recommended, because it allows you to define which audio files contribute to the Smart Tempo analysis, and allows the analysis results to be shared between all audio files. In cases where you do not want the Smart Tempo analysis results to be shared across audio files, and in which the project contains a single region having a clearly audible and consistent rhythmic pattern throughout (for example, a stereo recording of the overhead mics of a drum kit), you can use the following workflow:
After opening the project, make sure the Project Tempo mode is set to Keep, and open the audio file corresponding to the rhythmic region PDF
Logic Pro Instruments: PDF