Browser NS_ERROR_NET_RESET [closed]

Question

I have two boxes:

A: IIS 8.5.9600 on Windows Server 2012 R2

B: IIS 8.0.9200 on Windows Server 2012

php version is the same: 7.4.13

when a simple php script in box A outputs more than 4MB I get in the browser: NS_ERROR_NET_RESET

On the other hand, this does not happen on Box B, it seems immune.

I have narrowed down it happening when just a simple query from the db brings a 7MB text, but the problem occurs as soon as I pass 4MB.

but the query is not necessary, even this simple script causes the problem:

$s = str_repeat("a", 4200000);
//just a string with length slightly more than 4MB
echo $s;

So it happens when the output from php is larger than 4MB

• (IIS) maxAllowedContentLength is at 30MB so not an issue (checked it in iis manager)
• (PHP) memory_limit = 256MB so not an issue (checked it in php.ini)

edit: the error i get in IIS error logs is Request_Cancelled

How can I further find out the root of the problem and solve this?

Thank you in advance