My Johnson Controller lost its 56

Seems to still be reading accurately otherwise and the probe passes its resistance test, but when temp rises past 55 to hit 56, the unit reads 57. I think it holds to 57 until the temp actually makes it to 58. I haven't found any other missing numbers from low 50s to low 70s. It's hard to say whether it is a new problem since this is the first time I've chosen to keep something at 56 (cutting in at 57, cutting out at 55), so I probably wouldn't have noticed.

Any similar experiences or ideas out there?