Sigma 14.16 STS screen barely visible
Several reason come to my mind:


The temperature at which you were using it. LCD displays get notoriously slow at low temperatures. You mention -8°, was it right then when this happened? Things should go back to normal at room temperature. The computer will still be working normally but the display literally freezes. The phenomenon is well known to people who own an early LCD wristwatch. They became unreadable in the cold.


At low temperatures, the battery either 3V lithium CR-type cell or Li-ion rechargeable slow down because of chemistry slowing. 
If the battery is a CR-cell it might be reaching the end of its life. Your device may be new but the battery was already inside for a while when you bought the computer or the cell is faulty.Try replacing the battery.



But then since your device is quite new I'd advise you to take it back to shop who sold it to you as warranty is still applicable.