Photos for Mac slideshows

I am trying to create a saved slideshow from an album, but my carefully sequenced selection of photos is completed mixed up when I click the Create button. I went into projects,created an empty slideshow, and made a fresh selection using the Add button, but the chronological order was again jumbled up. How can this be overcome? This problem did not occur when I created previous slideshows, and I suspect it may be something to do with a recent update of Photos For Mac. I'm minded to try creating the slideshow in the iMovie app, but fear I'll get the same problem.