I am trying to create a slide show that has a different image frame size for each of the slides within it.
The images on each slide are different widths, I have a horizontal transition between each slide and want the amount of white that appears between images to appear consistent as it slides across which isn't the case if the frame width is the same across each one.
I have tried with the 'Edit together' box unchecked and with items on each page locked but it continues to change the frame size across all the pages whenever I alter any of the slides.
I’m not sure if it will achieve the effect you are looking for, but if you use a Composition Widget instead of a Slideshow Widget, you will have more control of the layout.
If you make heavy use of the OOUI (the blue arrow menu near the upper right of a selected object) you can get the various widgets to do some things that are very different than their names would suggest.