Recently one of our sites got suspended by Google Ads due to "Destination Not Working". When I talked with Google Support they told me that my site is not accessible from all location globally. Then I tried to investigate, the site is hosted on Google App Engine. And I didn't find any 500 errors. But sometimes some website checking tools like "Uptrends" showed me inconsistent error "Http Protocol Error"/500 error. Then I tried to see closely on Google stackdriver logging and ran several tests on Uptrends and on other tools. But I saw something like this.
And on App Engine logging, I saw something like -
And also sometimes some HTTP request is not hitting my app so my app logging is not working and it's bothering us so much. We are losing tons of our marketing budget due to this facts. So it would be great if anybody come forward and tell me any clue to test and help me to investigate.