SL360 project (.story) file = 30 MB, published (.zip) file = 200 MB. Help!!

I've been publishing quizzes authored on SL360 (as xAPI zip files for uploading to my LMS/LRS) for several months now, and have authored and published a few dozen of these without significant issues, but I've recently run into a problem which I can't seem to find the solution for.

Up to now, the project files I've been publishing from have had a file size comparable to that of the published zip file. However, my most recent project has a file size (for the .story project file) of around 30 MB, but when I publish it the zip file produced has a file size of around 200 MB!

It seems that most of this bloat is in the form of a large number of .png files located in the 'mobile' folder within the published zip file.

This project is no different to any of my previous projects in terms of the format or types of content contained within it (one scene containing a introductory slide, followed by a series of slides each of which is random question draw from a question bank, and a final results slide - no audio, no video, all just text and images).

Many of my previous projects contained far more question slides and images than this one and didn't balloon in size upon publishing like this one does.

I've spent the last few days looking through the knowledge base and forum to find a solution, and have tried a number of different things suggested there in similar cases but nothing is working.

I suspect this may have happened after the most recent updates - I've gone back to some of my previous projects and re-published them to see if they are affected by this problem, but they seem to be publishing to the same file sizes as before without ballooning in size like this one is.

I've started a support case, but in the meantime if anyone here has some suggestions I'd really appreciate it!