Strange behavior of Task submission in Appian v17.1

We are facing a strange behavior related to Task submission for the following scenario in Appian 17.1.

1. When user submitted the task of type (Adhoc task, Assigned task, Task initiated from Action (e.g. Start Form) etc), the task is getting submitted successfully from user end, but after a moment same task is re-appearing in the user's Tasks queue in tempo. In other words, user able to submit to same task multiple times. When I open the process instance in monitor mode for the same task, it is observed that the process is stuck at the task node and it is not getting completed. In actual, form is submitted, process variables are updated with the user input values. however, it is not flowing to next point in process instance. We also observed that process flow is flowing, if it is a activity chained, i.e. this issue is only occurred for non activity chaining...

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