Excel makes certain cells pink when sorting?

Using a project list spreadsheet. Columns are arranged: Job #, Name, City, State, Client, etc.

Sorted jobs based on Client. When doing this, certain "Job #" cells were formatted with a pink background/red text. This usually indicates that there is a duplicate cell, but having checked, there are no duplicate cells with the same value in them.

Why is excel formatting them when sorted, if there are no duplicates? How can I fix/turn this off? Or check what it thinks it is indicating?

Click on the Conditional Formatting button and select "Manage Rules".

In the box for "Show formatting rules for:" select "This Worksheet"

This will show you a list of all the conditional formatting rules that are set for that particular worksheet. You can then edit or delete the rules.