I'm trying to make a simple animation of a boundary progression over time in ArcGIS Pro. The data are a set of individual layers for a national boundary, each layer is a different time step. In the animation menu I'm setting keyframes, one for each time interval, turning each layer on in secession. In the Timeline window I see the correct keyframe thumbnails, and if I advance the frames manually from the Playback menu they change as expected. But, if I hit play on the Playback menu the screen goes blank and I just see the time slide moving but no map. If I export as a Draft or GIF I get export files with only the basemap showing, my layers are missing.
What is going on with my animation?