Hi Mark,
Thank you for sending us your files. I can see that you have used delay in the animation in the banner. We are aware that there is an issue in Safari with using the delay in timeline animation. Safari (at least in the latest version) does pause animations when the tab loses focus, but depending on whether the animation had a delay or not, and whether the tab lost focus while the animation was in its delay period, it doesn't restart the animation as expected, so in preview the animation looks broken.
One way to fix the file is to replace the delay with empty keyframes. I have done that in your file and your banner seems to work better now in Safari. Would you please download the attached file to your project folder and preview it in GWD again?
Thanks,
Emily (GWD Team)