ScheduleTask is not getting executed for some orchestrations

In our service, we have different orchestrations which handles Events. At the end of each orchestration we are scheduling a task to mark its completion - so that our service reports that the event has been handled successfully.

The method definition we are using is:
Task ScheduleTask(Type activityType, params object[] parameters);

We are seeing that for some orchestrations, ScheduleTask is not being invoked. This is leading to our service not reporting/probably not even completing all the orchestrations.
We are using v1.1.0.6 of the DurableTask lib with .NET 4.6.2