I had exact same problem with my Anova. Support came back with some suggestions. They said to clean the heating heating element, probe and impeller of calcium buildup. They also suggested to give the device a complete drying and resting (24 hours) and to try turning on and starting the Anova machine when it is out of the water bath, forcing an error to alarm. Then I was to put the device back into a pot of water and try setting the temp again. This was somehow to reset the error.
Alas it did not
More, it seemed to have killed the device entirely (the last bit, with switching it on dry, forcing the error - after that I can't turn it on at all. It's dead).
What's worse, Anova refused to help any further, because my device is not under warranty anymore. Admittedly yes, it isn't, as I bought it in May last year, however it was only used a handful of times when I first bought it and then it spent months unused in a cupboard. You would think a device such as this is built to take way more usage before giving up the ghost, but clearly not. Shame that Anova was not willing to be more helpful... I feel truly let down. And I will definitely not be buying again!