Why are Images Imported as Planes Hidden by a Reference or Background Image? When I import an image as plane with the alpha channel for transparency, and it is in front of a background or reference image I can't see the object (plane) to place or edit it? Why is this? 

If this is a duplicate question please link / flag, I have looked but can't seem to find an answer... Thank you for any help you can offer.
This happens because Images as Planes addon automatically uses Alpha Blend mode.

Switch to Alpha Clip or Alpha Hashed and it will work as intended
(You need to be in Eevee, for these options to show up.)