If you use Revit 2020 (yes) with BIM 360 Design (yes) and migrated projects (yes) with lots of families (yes) don’t delay installing this hotfix (which will be offered in the Autodesk Desktop App). It fixes a corruption which could result in data loss.
Fixed an issue that resulted in the loss of family data in some workshared models when family definitions had not been recently modified. This fix does not repair models which have encountered loss of family data, for more information refer to Family Corruption in Revit 2020.2
Clipped from: https://help.autodesk.com/view/RVT/2020/ENU/?guid=RevitReleaseNotes_2020updates_2020_2_1_html
