Having problems with my back buttons. Either they don’t work, or they jump to the next slide.

I’ve input the criteria:

1. Back buttons
2. Transparent
3. Go to previous slide
4. Timing 3 Timing/0 appear after/1.5 pause after
5. There are no click boxes covering the button

Note:  I have lots of other slides that work perfectly well.  I’ve cross referenced the properties / timing/ style/ ect to ensure that everything is the same.  I’ve actually deleted the malfunctioning ones and reinserted them again, but to know avail.

Please help!