I’m facing an issue with my React frontend and AWS Lambda backend setup.

When my app makes multiple API calls at the same time, some of them randomly return a 500 Internal Server Error, while others succeed. On the next attempt, the previously failed APIs might work, and a few different ones fail instead there’s no consistent pattern.

Here’s an example response from the browser network tab:

Request URL: https://api.example.com/account/night-audit/business-config
Request Method: GET
Status Code: 500 Internal Server Error
x-amzn-errortype: InternalServerErrorException
x-amzn-requestid: ba6476cd-4310-4eaf-9333-d41123e6654f

I also checked the backend logs in AWS CloudWatch, and for these failed requests, the Lambda function was never triggered, meaning the request didn’t even reach the function handler.

Setup:

• Frontend: ReactJS
• Backend: AWS Lambda (Node.js)
• API Gateway in front of Lambda
• HTTPS endpoint (dev environment)

What I’ve observed:

• The same APIs sometimes succeed and sometimes fail.
• The failed APIs return 500 InternalServerErrorException.
• No corresponding Lambda logs for failed requests.

My Question:

• What could cause intermittent 500 Internal Server Error responses from API Gateway when the Lambda function isn’t even invoked?
• Could this be related to API Gateway limits, throttling, cold starts, or concurrency issues?