The Hotfix is recommended as follows:
If you have experienced instability issues with multiple instance of ArhiCAD or problems with Zone calculations we strongly recommend applying this ArchiCAD 16 hotfix.
The hotfix applies to all components: ArchiCAD, BIM Server, BIM Server Manager, EcoDesigner, BIM Explorer, MEP Modeler and all other GRAPHISOFT-distributed Add-Ons and Goodies. It applies to all (Commercial, Educational and Trial) license types.
For a detailed breakdown of installation notes, bugfixes and more, visit the full update page here...