Before RoonOS build 254 that was released last fall, it used the older Linux driver for NTFS. This one had some issues because NTFS is a proprietary and questionably documented file system. It’s a bad idea to use it with Linux for anything important, and the ROCK documentation specifically recommends (and always did) against using it for external disks that are connected to ROCK.
It’s entirely possible that occasional errors occurred without doing anything specific, simply caused by bugs in the Linux driver.
Since RoonOS build 254, it uses the new driver that was added to the Linux kernel in spring 2022, made possible by a generous (and surprising) donation of code by Paragon Software, who had invested lots of efforts into reverse engineering NTFS.
This new driver is much more strict about NTFS file systems being error free (which is important to guard against later corruption), and after the RoonOS update there were lots of cases on the forum where the new driver refused to mount disks that the older RoonOS had accepted. One cause of such refusal was unsafely removing (simply unplugging) the drive from the Windows machine.
Therefore, it’s entirely reasonable to try and rule out first that your issue belongs to the same family.
I could have asked again. I’m glad you found the issue eventually!