Opus supports animated GIFs via the Video tool, not via the Image tool.
If you load an animated GIF with the Image tool only the first frame will be displayed and it will not animate.
Inserting an animated Gif using the Video tool allows you the same controls over the animation as with other video formats and is more versatile.
Technical Note:
Opus does not support animated GIFs without a global palette. Although these files will display successfully in the editor they will not appear properly in the published version of your file.
If you find that animated GIFs do not work properly in the published version of your project you can apply a global palette to them by loading them into Animation Shop and saving them out again with the default settings.