When you annotate an object with obfuscation like here:
Sometimes you create partial masks or polygons as something in front is "breaking up" the annotation in the background. However, this is less-than-optimal for machine learning networks as it causes confusion. To that, you can either create the background annotation as one uniform annotation using the brush like this:
Or you can merge separate masks or polygons into one shape by first selecting all of them, and then click "Merge into single mask" (at the top in the annotation view).
The final result will be a uniform mask (if you selected multiple polygons, we will convert them to one mask annotation, as polygons should never be used to annotate multiple regions) like here: