Php5.6 + apache Why does apache return 500 when accessing $_POST?

Question

PHP

When submitting a form by POST, it suddenly began to give 500 by the web server
Previously, everything was fine,
Now the code is executed exactly to the place where the $_POST variable is accessed, if it is filled, then 500 is immediately issued, even with the usual isset($_POST), or sizeof( $_POST)
I sinned about the POST length limits, but I checked it even on the simplest form, it stopped working

Answer 1

problem found,
MaxRequestLen overlaps max_post_size