Assume displayExceptions is true.

If in the exception stack trace a function argument contains binary data that json_encode could not handle, then json_encode will return false. As a result the response content is empty.

This happens at following lines:
RenderErrorListener.php#L94
ApiProblemResponse.php#L59

This situation can occur in various debugging scenarios, e.g. uploading a file and passing its blob to a function, and it can be pretty difficult to overcome because the empty response.

Proposed solution
A better choice would be to use \Zend\Json\Encoder::encode because it can correctly handle the encoding of binary data that json_encode can not encode.

// Assuming $data['blob'] contains the binary data of a PDF file

json_encode($data); // return false

\Zend\Json\Json::encode($data); // return false if the json extension is available, otherwise \Zend\Json\Encoder::encode is used

\Zend\Json\Encoder::encode($data); // return the encoded json