If you have time machine versions of these things, I’d be happy to take a look at the internals of the files and report on what is different between them.
Almost all the real file size of an larger RW project is in the media – the images stored in the project. So, my guess would be that it has do with a change that has been made recently to the images.
However, without more data on the subject, I don’t know that it’s productive to guess at what else might be the cause. If you send me the before and after files I can give provide you more detail by looking at their internals a bit.
If you’d like you can sign on to http://slack.yourhead.com/ and send each project file zipped in a private message to me there.
I have zipped up a copy of my current RW6 project and a restored copy from the 22-AUG-15 (93Mb & 126Mb) and uploaded to you on Slack for you to compare.
And for those following along, it looks like a small optimization (removing old unused images) that we made in S3 had a large impact on these particular projects. All is verified as A-OK. Thanks Heppys_Golf for sending the files so quickly!!!