So I finally sat down to look at what was wrong with the HC-SR04 sensors, and the discovery was quite interesting: it turns out it’s a capacitor on the circuit board that went bad, replacing that capacitor fixed the defective sensors. My suspicion is that this batch of sensors are technically HC-SR04P, rated for 3.3V to 5V (the original HC-SR04 is rated for 5V only). My guess is that the manufacturer assumed anyone who buy these are only using it under 3.3V (otherwise you would have chosen the original HC-SR04, which is the same price). As a result, they may have used subpar capacitors which are not rated for 5V. On OpenGarage the power pin of the distance sensor is still connected to 5V, so that may have resulted in the capacitor failing over time. This is really annoying, but at least we figured out what went wrong. We had several returned OG that had similar symptoms (distance stuck at 3 to 5cm). After replacing that capacitor they all went back to function normally. A small capacitor makes a huge deal…