Probably not your problem, but something to look out for just the same, ... the older LMxx I2C temperature sensors had a minimum I2C temperature query time. That means you could not request a temperature immediately after a previous one. You had to leave a quiet period for the internal A/D conversion. If you read the part too often, it would give you the LAST reading only and abort the current conversion. You get stuck reading the same old stale data over and over again. Something about 100ms between reads was required (check the data sheet). Anyway, that could account for errors if your program reads it too often in some cases.

GB