I'm using 2017 PS CC
Ive created an animation and when I play it it works absolutely fine. However, when I 'save for web (legacy)' I can't preview the animation - only the first frame shows. And when I go ahead an save, again, only the static first image is visible - no animation.
You've posted in the Lounge, which is for non-technical discussions. I'll move this to the Photoshop forum.
Is your animation time-based? You'll need to convert to frame-based to be able to save it as a GIF. See here for complete instructions on creating an animated GIF in Photoshop: