How are you uploading? From the Web UI? Via one of the official clients? Via something else?
Also please post the actual full raw log entry. We need the stack trace.
And it would also be helpful if you checked your browser inspector.
These items were all noted in the support template, which perhaps you overlooked? 
PHP_UPLOAD_LIMIT in the image already sets both post_max_size and upload_max_filesize simultaneously.