Content-Length missing randomly?

Hi,

Can someone tell me the Content-Length response header usage?

It seems it “randomly” goes missing on responses.

Taking this as an example

https://api.github.com/repos/Rinnegatamante/DaedalusX64-vitaGL-Compatibility/issues?state=open&page=1&per_page=100

Three requests, it appears and then dissapears.

content1.png content2.png content3.png