Thanks so much for looking into this Jim!
Yes - this example was sloppy and should have been exactly level, not 16 pixels out.
The bottom Weemol group is necessary because I wanted the left image (wine bottles) to remain in place as the right image (house) slid over it - with that bottom group turned off the bottles disappear as soon as the other image begins to expand, which isn't exactly what I want. The only way (non programming) around this seemed the clumsy solution of having 2 copies of the wine bottle, 1 above and one below the house, with opacity or display adjusted as needed depending what part of the timeline you're on.
Ultimately, there will be 4 images that slide over each other so perhaps making the other 3 just disappear will be easier anyway.
I came to the same conclusion as you - I moved triggers and timeline keyframes apart by a frame and that seemed to solve functionality issues.
I've now come across a new issue that I think may be a bug - when you take the symbol I created and animate its scale on the main timeline going from 10% to 100% the images become totally blurry!
It's as though Hype is taking the first 10% scale and using that pixel size throughout! I tested this on your version in the hope that it's something to do with me but the problem remains - here is an edit of your file where you can see the problem - is this a bug?
SlidingTest_JHSv2.hype.zip (283.3 KB)
Thanks again for your time, much appreciated.