Same problem here. 20pcs tested with the same result.
It was noted that the 0.5V reacts with the change in current, which is beneficial in my application since I can connect the sensor to a 3.3v microcontroller and have the values within the range of the uC.
Another thing to note is that (at least the units I received) is operating at 3.3v with identical output voltage as when it was connected to 5V.
Further testing leads us to believe that this specific IC is a clone of ACS712. For reference the batch number we have are all 16329
I can connect the sensor to my AD converter (waveshare) successfully.
But I can measure correctly only when current go in one direction (volts raise from 0.5v) not in the opposte: the output is not symmetric.
It seems that I'm not yet entitled to post real time in this forum. If my previous reply does not get posted, here's the summary: This is not an ACS712 chip. Although the IC show ACS712, it is actually an ACS713. It is only unidirectional with zero current at VCC*0.1