I'm not clear what you are using to encode or decode, whether it's even related to this project. You haven't given an example of the QR code

@srowen My mistake. We are using the ZXing library for scanning QR codes in Android. In essence it's like this:

// Initialization of the MultiFormatReader
Map<DecodeHintType, Object> hints = new EnumMap<>(DecodeHintType.class);
Collection<BarcodeFormat> decodeFormats = EnumSet.noneOf(BarcodeFormat.class);
decodeFormats.add(BarcodeFormat.CODE_128);
decodeFormats.add(BarcodeFormat.QR_CODE);
hints.put(DecodeHintType.POSSIBLE_FORMATS, getFormats());
MultiFormatReader reader = new MultiFormatReader();
reader.setHints(hints);

// Decoding a bitmap from the camera
protected void decode(BinaryBitmap bitmap, int width, int height) {
    Result rawResult = reader.decodeWithState(bitmap);
    String retval = rawResult.getText();
    Log.d(TAG, "Scanned: " + retval);
}

The Log.d() line at the end prints the raw string that was in the QR code. Basically if we scan a QR code that contains a JSON string, some devices produce the JSON string with extraneous characters while some don't.

You haven't shown evidence that the decoding is the problem. The QR code probably has the text it says it does, right?

@srowen I'm not sure I follow. The output of the decoding varies from device to device when the input and the whole codebase remains the same.

That's a function, likely, of the platform character set and how it renders the chars. The (?) chars mean unprintable. But they really are in the QR code, likely.

@srowen They are not part of the QR code.

You haven't posted any QR code, so I don't think we know that. It's the most likely explanation. Why not examine the code and encoder first?

@srowen You can try any QR code generator and type the JSON I mentioned.

Works OK for me:

https://zxing.org/w/chart?cht=qr&chs=350x350&chld=L&choe=UTF-8&chl=%7B%22foo%22%3A+%22bar%22%7D

http://zxing.org/w/decode?u=https%3A%2F%2Fzxing.org%2Fw%2Fchart%3Fcht%3Dqr%26chs%3D350x350%26chld%3DL%26choe%3DUTF-8%26chl%3D%257B%2522foo%2522%253A%2B%2522bar%2522%257D

It's an issue with your code and how you're constructing text to display, or an issue with your encoder. This project's encoder/decoder appear to be fine.

Does Zxing work only in Android? Do we need to conditionally check for other mobile OS's like iOS and Windows?