Seamless Pattern Showing Seams

Using PSE 14.  For the past couple of weeks, I have noticed that new patterns, which I create, are showing a seam.  I have never had this problem before, so don't understand why.  I have recreated patterns over and over, because I've assumed I have done something wrong.  I get the same result.  I suspect this is a bug after a recent update or could it be one of my settings?  Patterns I've produced prior to the last few weeks all work fine, so something has changed. Can anyone point me in the right direction?

Here is a screenshot of my pattern and the result when used (note: you can see borders on the screenshots which are not part of the pattern.  I was just a bit sloppy when selecting the screenshot)

Any help would be appreciated.  I'm getting desperate!