A workflow activity is waiting for an external event or approval that never arrives, such as an email response or manual approval action. (high likelihood)
Worker node crashed or became unresponsive while processing the workflow activity, leaving the context orphaned in executing state. (high likelihood)
Timer activity is stuck due to system clock issues, timezone problems, or scheduler service disruption preventing proper timer execution. (medium likelihood)
Workflow activity script contains infinite loop or blocking operation that prevents the activity from completing normally. (medium likelihood)
Database locks or transaction deadlocks preventing the workflow context from updating its state in the wf_context table. (low likelihood)