Audio Not Working on Some Projects

Good day,

I'm making a course that has 5 stages, so 5 projects.  I'm adding audio into slides and in three of the five projects no problem with playing the sound automatically or by activating it by a button.  In two of the projects the sound will not play.  For the life of me I can't see why sound will work in only 3 out of 5 projects.  Perhaps I'm missing a setting?  On the playbar under the timeline, the mute is not turned on.  Thanks for any ideas as I'm stumped.

Dave