(The email I sent:)
Hello! I want to report a serious glitch and ask for help if you can offer it. I'm having a rough time with one of my character drawings.
I'm using an iPhone 5s on version 10.2.1.
I spent a lot of time drawing a character in the drawing interface, but at some point it stopped letting me draw, like it had "run out of ink"--I'd draw one stroke of any kind and then it wouldn't let me draw any more. I pressed "undo" multiple times to try again, this time conserving ink. Pressing "undo" once erased multiple strokes, then continued back to erasing single strokes. Very strange.
I finished the drawing, adding eyes, mouth, fingers, toes, and wing details. These were drawn in black. I saved it and tested it out, only to find that all these details I'd added were changed to red (which I'd been drawing in before black) and looked sort of droopy. (I'd say it looked like blood, which was quite creepy, but also a coincidence and technically irrelevant.)
I posted the drawing online to see if I could fix it, but strange red lines appeared between all of the added details that had turned red, in the order I drew them. (Again, creepy, but also, irrelevant.)
{Picture of character with red lines through it}
I downloaded the picture to edit it. I used the "undo" function and all the details that had turned red were erased completely, in one "undo". (I uploaded this as well, in hopes of editing it, but it did that "out of ink" thing again)
{Picture of WIP character with no features}
Seen here, pants coloring, added details (face, fingers, etc) and some hair color were erased in one "undo".