I suddenly have a blank preview and can't scrub in the timeline
First, check whether your project is set to 59.94 fps (open Help/Settings). If so, try changing to 60fps, then force-close and restart LumaFusion. This may resolve your issue. If not, you may also want to try lowering the preview quality (open Help/Settings and tap on Preferences).
Please contact us at firstname.lastname@example.org if neither of these recover you preview, or if you find that nearly any edit within a project loses the preview again and again.