Cannot select items in backpack/switch items around in Norse Mythology Mashup

I've only recently (1 week) started playing with my young son on our Samsung Galaxy E 9.6" tablet. As of Friday, April 6 while playing the Norse Mythology Mash-Up world (and also on vanilla minecraft worlds) I am unable to select items in my backpack (only successful with items on hotbar) to switch them around, craft or move to the hotbar. Items once moved into the furnace for crafting just go in and sit there doing nothing. I can, however, move things from inventory into a chest, but cannot move stacks (only single items). I've tried adjusting various settings, logging out and restarting tablet/game, and even deleting game and reinstalling to no effect. This has really ruined my son's expectations for our first weekend playing together. Thank you for looking into this matter.