I’ve had this issue happen a few times now on my phone. When I’m doing reviews if I put the wrong reading in more than once (for example two different kun’yomi readings) the text that says Wanikani is looking for the on’yomi reading sticks to the screen so that if I subsequently type a wrong answer I cannot tap the show answer button because of this reading tip.
I’m using Chrome 76.0.3809.111 on a Pixel XL phone running on Android 9.