Third article for same category doesn't show until fourth added.

I added two articles for Relief Society, checked the display by category, saw both under either category selection (All or Relief Society). Then added another for Relief Society, then displayed for Relief Society category and only saw the first two articles. But the third one did show up when changed to display All categories. Tried several things without success, but when I added a fourth article for Relief Society, the 3rd and 4th both showed up with the others in the display.

We have been unable to duplicate this problem. Can you provide any further information please?

Thanks
Mindie