AWS Lambda execution leaks occur when executing code runs in a different invocation than the original execution context, creating complexity and potential bugs. This can happen with async handlers using the `require-await` rule or callback-based handlers, which never return a value to the AWS Runtime. To avoid these leaks, use ESLint's `require-await` rule and avoid callbacks in favor of async Promise constructs, such as using `util.promisify` to convert callback-based functions to promise-based async functions. By following these best practices, you can prevent event leaks and ensure deterministic executions in your Nodejs AWS Lambda handler.