I can confirm that there is a difference between what Sozi shows and what I get in a web browser when opening your presentation. Interestingly, when I change the aspect ratio of the browser window, I can get the desired result.
Here is a possible explanation:
The editor and the player use different data to position and scale the layers. The editor computes a layer's geometry relative to an "anchor" object, so that it can reposition that layer automatically when you move or rescale things in your SVG. The editor saves the layer info to the presentation file as absolute coordinates, and this is what the player uses in the web browser.
In your case, I think that the absolute and relative data are inconsistent, possibly because in some frames, the "anchor" object is a horizontal or vertical line, with a width or height equal to zero.
This never happens in my own presentations because I usually use rectangles to delimit my frames. This is something you can do as a workaround before this issue is fixed.