Typing a plus sign (+) or a backslash (\) into the cloze field causes the Android app to crash. This does not happen in Windows on Firefox or Chrome.
Note that it’s easy to type such characters by mistake. For instance, I use a Russian keyboard mapping that doesn’t match the characters printed on my English keyboards. Not only does this mean that I have to rely on “muscle memory” to hit the right key, but the mappings differ slightly between my Android and my Windows devices, making it all too easy to type the wrong character into a field.