Changed the first style preset to have yellow fill and stroke color
Draw an ellipse into the first page
With the annotation selected, click the style button in the annotation popup to open the annotation style popup
Change the opacity for that annotation to 50%
Click the cog menu button (top right corener) to open the menu overlay
Click the print button without changing any setting
At this point, it shows the annotation (print preview) as expected.
It looks like there is something not working properly with the way you are binding the right panel settings with WebViewer. Do you perhaps have event listener when the annotation is selected that overrides the previous opacity configuration?