UPDATE: With 55 views and only one response, this must be a unique problem. I kept comparing the oddly saved version with an earlier version that operated correctly and stumbled across "revert" menu, which allowed me to revert to an earlier saved version of the project I had trouble with.
Fortunately, it corrected the tempo as well as the alignment of the tracks. It was so strange that the tempo read correctly at 130 bpm, but in fact was playing more like 126bpm. I had tried changing the tempo up and down to see if it would come back correctly; I tried restarting Logic, and then my computer, but nothing worked.
And, an additional anomaly is that several of the tracks had moved horizontally so they were no longer in alignment with the downbeat of the song. I had recently updated the OS as well as Logic Pro, but none of the other projects I'm working with have suffered this odd occurrence.
I'm hoping this is just a "ghost in the machine" one-time oddball happening! Thanks to all of you who read my question. Maybe "revert" will help you in the future.