If I had to guess the backspace bug is usually the Android keyboard. Gboard sends composition events instead of keydown events, and a lot of web UIs only listen for keydown. Switching off predictive text or trying a different keyboard fixed it for me.

Otherwise you can use agy on the Cosyra mobile app, its far better. I'm not going to claim its better than the Claude app, but its certainly better than the Gemini RC.