Has anyone else noticed rather unexpected behaviour of the the LR6 slideshow pan and zoom feature? Based on my testing, it seems like the pan and zoom feature produces a different effect each time the feature is activated. For example, an exported video will not be identical to its preview. Another example is that it is nearly impossible to generate a slideshow at multiple video resolutions (e.g. 1080p and 720p) since the pan and zoom effects will not be identical. A workaround would be to use a video conversion program to process the highest resolution video, however, this leads to some quality reduction as compared to generating the (lower resolution) slideshow directly with LR.
If my assessment is correct, I suggest adding a button to only change the pan and zoom following explicit user action. This would permit a consistent pan and zoom effect if desired.