Azure Stream Analytics is too slow - also time values are irrelavant
There is a latency when merging all the event in chronological order from the Event Hub.
ASA will visit all partitions from EH, get the data and organize the events into chronological order. This means that data must arrive at all partitions in the EH. I think this will also explain the strange behavior you are seeing with the EventProcessedUtcTime, it might be that because the events are ordered, the logical processing time is before the actual arrival time. Although I'm unsure about this because I do not know the inner workings of ASA.
This latency will increase with the number of partitions used, especially when the dataflow is slow.
You can sidestep the merger by partitioning on the field partitionid from EH.Make sure you are sending the data to the correct partition in EH as well.
More information can be found here at the Stream Analytics blog.