Okay, I've been using AutoCAD since 1987 and I'm not an idiot. Yet to this day, I can't understand why certain toolbars disappear in AutoCAD and I waste numerous hours trying to get them back. The last two years its the Vault toolbar in the AutoCAD Classic workspace. Everything says it should be floating. When AutoCAD first fired up, the toolbar even showed and now its gone. When I try to dock it, the other toolbars make room for it, but nothing appears. I know this is a Vault toolbar, but I've had the same issue with others. I hope someone can help be out here because it is driving me crazy.
Most of the time UI issues, especially those with elements not showing up/not staying in the same place, are workspace related. When you make a change to your workspace (e.g. showing a different toolbar), make sure the changes are saved to the workspace. Also make sure the workspace is current - AutoCAD will attempt to load the last workspace on start-up unless its told otherwise. Its also important to know where your workspace is being loaded from and saved to.