> For the complete documentation index, see [llms.txt](https://stephen-tsoi.gitbook.io/stephen-tsoi-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://stephen-tsoi.gitbook.io/stephen-tsoi-docs/messaging-troubleshooting/a-missing-event-among-billions-how-we-found-it-on-an-event-mesh/day-5-13-trouble-shooting-on-the-application-side.md).
# Day 5/13 Trouble Shooting on the Application Side
If you cannot find the issue from the broker's setting, consider yourself lucky because you are about to embark on a magical and wonderful journey. This journey will be a challenging and will require more than ten hours of work under pressure.
It’s challenging because you need to analyze thousands of lines from the application debug log to find the pattern, and there is no unique key between the application log and client messaging library log.
The event message loss can be due to **various reasons** related to the **application logic**, **architecture design**, or **product behavior**. In most cases, we can only trace and identify the root cause when the publisher enables persistent delivery mode and debug level logging. Let’s see some common errors below diagram.
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