When creating a pattern in CorelDRAW, it is important to make sure that the artwork is properly aligned. If it is not properly aligned, this can cause the white line.
If we use Pixel view (View > Pixels) and zoom in on this design, you can see that object is not properly aligned to the pixel grid. This causes the edge to be anti-aliased and results in a white line going through the tiled pattern.
To fix this, first go to Window > Dockers and select the Align and Distribute docker. Now select the patterned object and click on the Align with Pixel Grid button on the docker. This will shift the object slightly so that when you tile this pattern object, you will not get the white lines.
Learn more about aligning objects in our full tutorial How to Align and Position Objects.
Learn more about the pixel grid in our full tutorial Creating Pixel-perfect Graphics.
You can also find the CorelDRAW Q&A video here on the Discovery Center, where we answer more questions submitted by CorelDRAW users