There are a number of ways to determine what is happening with the plugin in CRM application if the problem occurs outside of the database layer.
The first is analysis of plug-in performance. For plug-ins operating in the sandbox, plug-in statistics can be queried for within the application to give an indication of how often the plug-in is running, and statistics on how long it typically takes to run. A plug-in type statistics stores information about the run-time behavior of a plug-in type and other statistical information. This entity is used by the platform to record execution statistics for plug-ins registered in the sandbox (isolation mode). The schema name for this entity is PluginTypeStatistic.
When certain errors are occurring, using the server trace files to understand where related problems may be occurring in the platform can also be useful.