Wordpress wp-json returns with net::ERR_EMPTY_RESPONSE

Question

I have a weird issue while adding new post but it returns with net::ERR_EMPTY_RESPONSE error. Please bear in mind that it happens after on certian length of post. My exact url is on admin side that has issue is:

/blogs/wp-json/wp/v2/posts/xxxx/autosaves?_locale=user net::ERR_EMPTY_RESPONSE

It happens on this line:

I tried with :

1. fresh copy of wordpress 6.4.1
2. Fresh database
3. No plugins install
4. Tried downgrading wordpress version to 6.2
5. checked file / directory permissions
6. I installed on localhost it works fine
7. Adding memory, execution time limits in php.ini also in .htaccess

I have virtual server so help on server side also be appriciated. I have also tried on different computers in different browsers.