I have a feeling it’s related to this message:
Oct 13 08:47:45 osmc udisks-glue[378]: Device /dev/sda1 did not match any rules.
A search for this message always pointed back to the OMC forum, so it seems to be an OSMC-specific message.
This post, from Sept 2015, says that the message “means that the file system type could not be determined by udisks”. Perhaps @sam_nazarko can cast his mind back and recall what situations might cause udisks to be unable to determine the file system type.
That said, could you try this quick test. Reboot with the ADATA disk disconnected, plug it in, wait 20-30 seconds and run df. If it’s not shown as mounted, then try manually mounting it:
sudo mkdir /mnt/test
sudo mount -t ntfs-3g /dev/sda1 /mnt/test
df