Upsert Endpoint Frequently Creating Duplicate Records

Recently (within the last 3-4 weeks) the Object Upsert API Endpoint has started to create duplicate records, specifically Tasks, Stops and Legs

This is not always an issue, I am seeing more and more frequently, I am seeing the upsert record endpoint insert Delivery Stops for example, 3-4 times without cleaning up

Why has this started occurring? It was not an issue until the last month or so