TransformStream throwing TypeError: Response body object should not be disturbed or locked

Question

I am using langchain.js streamEvents for streaming events to frontend. The intermediate steps output some sensitive data that I want to strip away before forwarding the stream so I am using the following transformer.

Reference: https://github.com/langchain-ai/langserve/discussions/531

Once in a while the code throws an error TypeError: Response body object should not be disturbed or locked that I am unable to decipher.

const transformStream = new TransformStream({
    transform(chunk, controller) {
        try {
            const text = new TextDecoder().decode(chunk);
            const lines = text.split('\n');
            
            for (let i = 0; i < lines.length; i++) {
                if (lines[i].startsWith('data:')) {
                    const data = JSON.parse(lines[i].slice(5));
                    delete data.data.input;
                    if (typeof data.data.output === 'object') {
                        delete data.data.output.context;
                        delete data.data.output.question;
                    }
                    lines[i] = `data: ${JSON.stringify(data)}`;
                }
            }
            
            controller.enqueue(new TextEncoder().encode(lines.join('\n')));
        } catch(_) {
            controller.enqueue(chunk);
        }
    }
});

I have attempted decoding and rencoding the stream after data transformation