Lines disappearing from Line Chart

Thanks in advance for checking this out ...

I copied a completed page with 7 visuals on it, working as expected, to the next tab and changed the field (X & Y) values.  The new page worked fine, so I repeated the same process several times, each time changing the source data fields for each visual.

For the line chart, on two of the twelve pages, it only displays the data points and one week on the X-axis - on two of the twelve pages.  The interesting point here is that when they were created, the lines appeared.  When the .pbix was reopened to do some additional work, the lines were gone and only one of the data points was listed.

I changed no settings, and in the visual format settings for the x-axis, the type is continuous for both.

I've checked the data, tried creating the same visual from scratch, and even deleted the page and duplicated a different page (they are all structurally identical, only the data changes) and got the same results.  

Any idea how to fix this or where I look to find a solution?

Thanks!

MNPBI