The most common cause of zero offset on a sensor is overload. Overloading beyond the sensors safe limit (usually 150% of rated capacity) deforms the transducer sensing element beyond its elastic limit so that when load is removed it does not spring back to its original form fully, resulting in an increased zero offset. A very brief overload, even one so fast that is does not register or isn't visible on the sensors associated instrumentation can cause this issue. Read our how to tell if my load cell is broken guide detailing how to check the zero balance.