This happens at least on Android Phones with no physical context buttons. To change context, dragging from the top or the side (orientation relative to runescape app) of the phone reveals an overlay. Clicking those buttons allows the phone user to switch apps or access the phone screen.
During the drag operation, a touch input is registered in the runescape mobile. Sometimes this opens a menu, sometimes this causes a movement or an interaction.
It can be extremely inconvenient to downright dangerous, especially considering most users are switching contexts very soon after this input happens. This error happens extremely frequently for me. Responding to text messages, changing music, accessing the internet--All of these I do often while playing Runescape, and it has become a serious pain-point of the app.
Pixel 2
Android 9
------------
As a side note, I've really been enjoying the mobile beta since I started it on the latest batch. Thanks for all the hard work!
14-Mar-2019 18:36:26