He doesn't look underweight so I'm guessing it's a combo of not eating enough by a little bit + he was full during the 174g and then empty during the 119g weight. At 6 mos I think 10 days apart is too far to be doing consistently. Once in a while when things get busy isn't the end of the world, but you should do your best to make sure he is eating every 7 days. Also could be the scale was malfunctioning one of the two times perhaps?