It can also be downright out of sight too. This is because it is rendered during the page change animation and the size changed by the time it is done rendering, and this doesn't triggers a repaint. Still, it's a rather major bug because you have to rotate the phone or resize the window to get rid of it
This project is unfortunately no longer maintained. If a new maintainer wants to step up and take care, the project is archived here: https://invent.kde.org/network/ring-kde You can just clone it in your private namespace on invent.kde.org and if you have started to work on it and fixed/implemented something get it reviewed and the project unarchived. Sorry for the inconveniences.