Recently Autodesk has released the latest installment of Revit 2019 and like with any software update it comes with some installation issues due to improper rights/privileges or 3rd party software. If you are missing content after installing Revit from the AEC Collection, try this fix that allows you to repair/reinstall your content libraries using the Windows Control Panel. Once you have repaired the install you can then launch Revit to check and see if your families have been loaded. You can also navigate to the local folder in the following path:
C:ProgramDataAutodeskRVT 2019LibrariesUS Imperial
Follow these steps:
In your Windows Control Panel, click on Program and Features to access a list of installed software on your system.
Scroll down in the list until you get to Autodesk Revit Content Libraries 20** (your version) and click Uninstall / Change.
Autodesk Revit Content Libraries Dialog box will launch with three options. You want to click on Repair and Reinstall to fix you missing content issue.