Confusing and inconsistent results are seen while testing a policy with similar filenames in a given timeframe.
It is best practice to upload your test file with a unique name including a date timestamp. Example, test1.420PM.txt, test2.422PM.txt.
While events are usually FI/FO (First In \First Out) there is no guarantee that it will always be the case.
A unique filename help support and the customer track the event from end to end.