Some users have experienced white squares appearing when working in Sketchbook. We call this "tiling" and have done some investigation to find out why this is happening.
It is due to devices running out of GPU and CPU. If your device is running too many apps, it starts to struggle. Some apps will be closed by your device once memory gets really low. Others won't even open. Sketchbook will remain open as long as it can. The white squares are indicators that your device is struggling and very low on processing memory.
To avoid this issue, we recommend closing apps running in the background that don't need to be open, opening up processing power for what you're currently working on. You can also shut down and restart your device to free up memory.
Finally, save often. If your device is running low on memory, eventually apps are likely to crash, and saving often helps protect you from losing work in progress.