I've been having this issue on my ipad pro for the past two+ months. Up until some major update, this wasn't a problem for me—my ipad could go to sleep and within 5-10 minute, I could turn it back on and the app would still be active and in sketch mode. Now, the app completely closes down the second I let my ipad go to sleep whether I'm sketching or typing. It's driving me insane because I can't always catch it or save every 5 seconds. I have to move to another sketching app because I rely on it every day for work and personal tasks. It just shouldn't be an issue that requires workarounds.