[Editor's note: to be more precise, MAX_FILE_SIZE can't exceed PHP_INT_MAX before PHP 7.1.]

Please note that the field MAX_FILE_SIZE cannot exceed 2147483647. Any greater value will lead to an upload error that will be displayed at the end of the upload

This is explained by the related C code :
if (!strcasecmp(param, "MAX_FILE_SIZE")) {
    max_file_size = atol(value);
}

The string is converted into a long int, which max value is... 2147483647

Seems to be corrected since php-7.1.0beta3 (https://github.com/php/php-src/commit/cb4c195f0b85ca5d91fee1ebe90105b8bb68356c)