@Tenda  Since you are saying you can freely navigate the NiFi UI when in this "stuck" state, NiFi is not stuck as both the UI and processor components all operate within the same JVM.  What you circled indicates that at the exact moment (last time browser refreshed) there were 24 active threads out of the 32 configured in the Max Timer Driven Thread pool settings.  Milliseconds later that could still be 24 active threads but consumed by different components.  The NiFi processors will all show small a small number in the upper right corner if they have an active threads, so step one is determining which processors are holding these 24 threads for a long time.  Then looking at those processors and the thread dumps to figure out why those threads are long running.  Typically we would see this when external service connections are made which are unstable, network issues, local NiFi repo I/O, NiFi CPU utilization, or long or very frequent GC pauses, or even OOMs.  So you have ruled out a few of these so far it sounds. If you found that the provided solution(s) assisted you with your query, please take a moment to login and click Accept as Solution below each response that helped. Thank you, Matt ... View more