I have had a similar issue.
I set my scale ranges and the symbology for each range, and somewhere along the line it breaks.
For instance, I have
1-5000
5000-10000
10000-15000
etc
and somewhere in my setup, the 1-5000 will adjust itself to 10000-15000 and now I have two symbols in the same scale and I cannot get them to move. I end up resetting and starting from scratch.
I have even tried right clicking on the bar and deleting a divider. The divider is deleted, however now one of the duplicate ranges extends itself to absorb the deleted segment, and the other duplicate remains the same.
Both attached screenshots are supposed to be the same. However, you can see the duplication and missing divider in Picture1. Picture2 is what it is supposed to look like.