Did the bag go down or did the opposite side rise
One of the sensors may be sticking
I have found that the sensors don't really fail other than they seem to corrode.
The bolt that the holds the sensor to the arm seems to be mild steel and the sleeve through the sensor is alloy possibly aluminium. After a period of time the alloy sleeve seems to corrode and stick to the metal bolt and this seems to throw up a fault as the sensor can't move.
After renewing a few sensors after little time, I now grease the bolt and sleeve on a regular basis, at least every three months and since doing this have not suffered and problems.
Saves having to replace the sensor at £40 a time.