Walls & Tiles / Mosaic can only display proper viewport previews when using the mapping mode "Per Object" mapping. When using "Real World" mapping mode, the viewport display is not correct, which is a known issue and unfortunately cannot be solved. The reason is that Walls & Tiles uses the open source map "BerconTile" and the mapping in Real World is not working correctly. The rendering though is correct, so if you want to use Real World mapping, you can do so, but without seeing a correct viewport preview. In this case you need to rely on the correct size settings for the bricks in Walls & Tiles or use "per Object" mapping instead. "per Object" mapping can easily be adjusted with correct mapping and settings by using the "Automatic Size" button, which calculates the correct number of rows based on the brick size settings and bounding box of the object. Make sure that the bounding box of the uv map covers the entire object before using the autosize button.