When you expose an app to the Internet using HTTP(S) Endpoints with External Placement will likely receive traffic from sources other than your intended users.

Some of this traffic may make requests for non-existent or non-sensical resources.

Cause

This is normal on the Internet, and there are various reasons it might happen:

Resolution

This traffic is usually harmless as long as your app does not expose major unpatched vulnerabilities.

So, the best thing you can do is to take a proactive security posture that includes secure code development practices, regular security assessment of your apps, and regular patching.