If you are having issues exporting the project, kindly check each slide if they are working properly. Click on each slide and see if they would appear on the slide preview pane and see if the animations would play (if it's an animated slide).
If the slide won't appear on the preview pane or the animations won't play, kindly try double clicking on the slide to refresh it. If double clicking still won't solve it, try recreating the slide.
Please see screenshot below: (Double click on each slide that's having the issue)