…built in battery
But in all seriousness hitting the reset button on the bottom of the device could in theory cause filesystem corruption. The norns device isn’t using an SD card - the cm3 module has a 4GB eMMC which has higher write throughput than an SD card and potentially different buffering characteristics as a result.
The fact that your SD card occasionally mounts read-only sound more like a system configuration thing. Forgive me for not knowing the specifics in the case of an rPI distro but most Linux/UNIX systems have the option of attempting to repair filesystem on boot if it wasn’t unmounted cleanly or to simply mount the filesystem read-only if it wasn’t cleanly unmounted. FWIW I suspect you might be running into the later situation - a system configured to be conservative and mount the fs read only.