Flow is getting stuck at Write to Datastore node. We tried to create a new one b

You can check one more thing,
Do you have any terminate node which executed before the process flow reaches that Write to DataStore node?

Siva's suggestion is a very good point, actually if you check the status of your process (via Process Details) when the node is hanging you can confirm if the scenario described by Siva is happening; if the process shows as Completed then that's is what is happening, a terminate node event is being hit before your Write to Data Store node.