Lance
Thank you for the response.
In previous versions of Arc I could just import that raster dataset as is without any problems. I did not have to do all the steps you did.
I tested this on 10.6.1 a while back, and if you have an Enterprise GDB, you can use Desktop to import the raster dataset as is, without doing your steps (Have to check this though, as I have reverted to 10.5.1) The last time I checked I was also pretty sure you also could not create mosaic datasets as well. I will install 10.6.1 later and check.
It just feels to me that there was a functionality change to 10.6.1...
So in short, I have just been trying to import a raster dataset (tiff file) into an Enterprise Geodatabase just like in previous versions. (Raster to Geodatabase tool) (Not raster catalog)