PeterPan321:
I'll have to check into that. But with the batter connected, as in my modules, it probably wouldn't happen. At least it seems to me, from the data sheet, that the transition from input voltage to battery voltage should not interfere with an I2C operation.
It can (will) happen when the battery gets low.
A good battery will last many years but eventually it will run down.
I use the status to determine if the time in the chip is valid and display something different (not the time) if the wordclock powers up and there is no valid time.
Also, the DS3231 has a few different modes related to battery power and power down modes.
I'm not familiar with the library you are using but you may want to run through the initialization to verify how that library is setting things up .
--- bill