Why is media Texture not displaying correctly?

Having moved my project from 4.12 to 4.15 I’ve had to rebuild a media texture that was working fine previously.

Now I cant resize it to fit the area I want it to.

In the small area of bsp (50x45x1.0) it looks like this:

But on a larger section of bsp (200x200x200) it looks OK and usable like this:

Having used both the geometry >> Alignment >> Align Surface Fit

and Surface properties >> Scale >> setting U and V values to 0.25

Neither seem to fix this, any ideas?