When an app does not receive requests for some time, it goes into cold start. Courier then makes several attempts to send events until the app "wakes up". When the app doesn’t “wake up” the requests to it can fail due to a timeout. As a result, it turns out that some events never seem to be sent. This is an intermittent behavior.

Find an app that is into cold start Follow its logs via OpenSearch Sometimes it is possible to see that one or more events will never be sent.

There is no workaround available.