Basically if you break you save in any way; which would seemingly require for you to try and edit your save manually in a text editor.
Those that are on Android seemingly would have no way of messing up their save (unless they had rooted their device or had an app that allowed them to access the ".toa-data" folder and messed up the saves from there in a text editor app).
For the specifics of messing up, it'd be along the lines of removing commas, curly braces or variables from places they're needed (or expected to be).
Also on the topic of what the OP said, the scene's QR code can be scanned with a barcode scanner app (which might not be possible for those playing from an android device; if they're playing from their phone or don't have a secondary device to scan the QR code with).