USB source path changing for External HDD

Hi,

I have frustratingly searched the net and cannot even find anyone with a similar problem.

Raspberry Pi 3, Retropie and Kodi with Aeon Nox Skin. Complete Raspberry Noob.

I manage to get my NTFS external HDD to mount and add the source via Root File System/Media/USB*
Problem is Raspberry keeps automatically changing the source path!! for example Media/USB1 to Media/USB3 and so on.

So… when I go to watch a movie from the main menu, i get a path invalid error as the Media source has changed without me knowing. Then I have to go and manually edit the existing source and add the new path.

(I think this happens when I power on/off or remove the HDD, which I need to do to add more movies)

Any help in super layman terms would be really appreciated