Artboard Has Same Number As Previous

In duplicating artboards  in Illustrator in Windows 10. Select Alt and drag to create a new artboard NO problem. My artboards go from 25, 27, 27, 28. I cannot get a 26. I have created a new artboard at the end and even tried to move it between 25 and 27 to create a 26 and Illustrator will not do it. I still get two 27 artboards. SO the secondary 27 will not export. I have to create one at the end and rename it. I've done this for years, WHAT is going on??? It's a glitch and how do I fix it?