headi | Customisable and automated HTTP header injection | TLS library

When I execute an action (upload a post request) on my website from my home network (Slow, less than 1Mb/s upload), the Chrome dev tool shows several XHR requests :

While when I execute the same action but this time from my 4G phone network (Quicker, around 10Mb/s upload), the chrome dev tool shows only one (sometimes 2) XHR requests :

How and why does it decides to split like that? Is it link with the fact that it is transfer-encoding chunked?

or maybe because of the keepalive timeout of 5?

The problem is that when there are those several XHR requests and that I reload the page before all the requests ends up to code 200 (which can take several minutes sometimes), I lose some data.

Thanks.

EDIT:

As asked in the comment, here is the code I use for this part (I tried to clean it a bit by removing the parts not related to the problem, hope it helps)

For exemple, if I update or add a "tag" to my note (my code is a note taking app "Evernote" type), the changed is trigered here in my index.php file :