Dropzone : Cannot upload big images to server (>5M)

I have the following settings in /etc/php/7.2/apache2/php.ini:

max_execution_time = 300
max_file_uploads = 20
memory_limit = 32M
post_max_size = 18M
upload_max_filesize = 20M

However, if I upload a file which the size is exceed 5M, I get the message:

The given data was invalid.

And when I put Dropzone's full error response, I can also see this message:

The file may not be greater than 5000 kilobytes.

When I change Dropzone option maxFilesize, it works with figure lower than 5M, but when it's greater than 5M, the upload is still limited to 5M.

Also, I have no upload size limitation in my .htaccess file.

Where else could this problem come from ?

via Chebli Mohamed