Hi Katherine!
I'm so sorry to hear you're experiencing this issue. I understand how frustrating this can be.
We're currently tracking an issue where the Player's Play/Pause button is unable to pause the timeline of slide layers. Essentially, the Play/Pause in the Player can only pause the timeline of objects that have been placed on the base layer.
In the meantime, I'd like to share the workaround my colleague Joe shared with another user who ran into this issue. I hope this is helpful!
I've added this thread to the bug report so we can notify you as soon as a fix is released.
If any other questions come up, please let us know!