EC2 Gateways broker access between your AWS resources and the internet, and so changes to the must be closely monitored and reviewed. Ensure that only planned changes are taking place.
If this change was not planned before hand, revert it and investigate the source of the change. If it was due to improper policies/procedures, consider modifying permissions to prevent this from happening again.
CIS AWS Benchmark 3.12: "Ensure a log metric filter and alarm exist for changes to network gateways"