2) It starts happening after some time a document is opened and it gets fixed by restarting the app so it could be a caching issue (?).
3) Happens randomly, the app seems to freeze for a moment and it won't mirror the canvas. Will report as I find out more. Edit: this time the mirroring worked but the app froze for a moment and the undo history was deleted.
4) To reproduce the issue do this: draw a line, swipe or press the home button to return to the iOS home, open Safari and randomly scroll a page then open Artstudio again. About 1 out of 3 times an "Editing Disabled" popup will show up and the undo/redo history will be wiped. It's worth pointing out that I'm currently on iOS 13 beta 3 re-release, so that might be the cause.