My pebble steel is only 3 weeks, and work fine. Except today : I stayed 25 minutes eating outside with the sun on me but not that hot (maybe 30° celsius, not much). I tried to access to my timeline and the display went crazy : lines, glitchs, compressed informations (3 timeline info insted of 2). Very scary for a new product.
The display went normal after 2 or 3 minutes in the shadow. Did you experienced the same problem on pebble steel as quick as me under the sun ?