I'm not sure if this the same issue, but I had to update the endpoint when creating a client for s3-object-lambda. This is a known issue and will be fixed soon, but in case you still experience it, you can try using these lines:

const client = new AWS.S3({ region: "us-east-1", endpoint: "s3-object-lambda.us-east-1.amazonaws.com"});

// Override the signing service name from s3 to s3-object-lambda so the signatures are valid.

client.__proto__.api.endpointPrefix = "s3-object-lambda";

Let me know if this helps!