If any of your negative keywords (list, campaign or adgroup negative keywords) use the modified broad match, you will see a warning on the dashboard to alert you to the fact that this match type is not supported for negative keywords. Using this match type for negative keywords can lead to inconsistent behavior.
Click on the dashboard warning above to be taken to the relevant screen with a grid showing those negative keywords at the top. You will see the alert symbol next to those keywords:
Or you can remove all the '+' signs in multiple keywords with a one button click by selecting the keywords and using the tool shown below:
In the case of list negative keywords, click on the number of keywords in a list to see the individual keywords: