Not sure if this is an issue on other devices but I find when playing on a Samsung device in order to minimise the game you have to swipe up the bottom of the screen to see and click the home button. But the swipe up action registers as a movement input ingame. So if your mining/woodcutting it often takes you off the resource and when you return to the game you realise your characters just been idling. Not an issue for combat if you have auto on as it resumes after the movement.
Not sure best fix but maybe that swipe movement can be ignored somehow or maybe the auto button could be cycled between off/combat/resources so you can auto farm resource and that movement doesn't matter.