Bytes in at Fully loaded is smaller than sum of sizes in the Page Elements list

Hi all,
I am using a local web page test instance running on AWS.
Recently I upgraded the agent to use the AMI: ami-a3a81dd0
The server instance continues to run using the AMI: ami-9978f6ee

Since the update, I have been getting strange results for pages with mp4 files.
For some pages, the “bytes in” value at Fully loaded is registering as 9,054 KB,
but in the “request details” table, the size of the MP4 file loaded on the page is
23,439.5 KB

My question is, why is the fully loaded bytes in value (which I’m assuming is the total size of the page) smaller than the size of the elements in the “request details” table?

Any help or suggestions of where to look would be most welcome!

All the best