If ETS does not start or takes too much time to update the 'Product Catalog Cache', then it could be that the 'ProductStore' folder contains invalid and/or inconsistent data. 

How to identify?

If you open with the notepad the 'ETS.log' from the directory '%LOCALAPPDATA%\KNX\ETS6\Log' and you find an error similar to that one:

2017-02-27 15:21:16,457 [1] ERROR System.Windows.Application - Autofac.Core.DependencyResolutionException: An exception was thrown while invoking the constructor 'Void .ctor(Knx.Ets.ViewModel.Application.Workspace.ICatalogService, Knx.Ets.ViewModel.Interfaces.IWizardDialogService, Knx.Ets.ViewModel.Interfaces.IOperationFactory, Knx.Ets.ViewModel.Interfaces.ILicenseAndAppManager, Knx.Ets.ViewModel.Interfaces.IEtsUserSettings, Knx.Ets.ViewModel.UISettings.ContentPanelSettings, Knx.Ets.ObjectModel.Project.Project, System.Func`3[System.Collections.Generic.IEnumerable`1[Knx.Ets.ObjectModel.Product.ICatalogItem],System.Action`1[Knx.Ets.ObjectModel.ProgressEventArgs],Knx.Ets.ObjectModel.Operations.IOperation], Knx.Ets.ViewModel.Interfaces.IProgressDialogService)' on type 'CatalogPanelViewModel'. ---> Ein Aufrufziel hat einen Ausnahmefehler verursacht. (See inner exception for details.) ---> System.Reflection.TargetInvocationException: Ein Aufrufziel hat einen Ausnahmefehler verursacht. ---> Autofac.Core.DependencyResolutionException: An exception was thrown while invoking the constructor 'Void .ctor(Knx.Ets.ObjectModel.MasterData.KnxMasterData, Knx.Ets.ObjectModel.IProductStore, Knx.Ets.ObjectModel.CatalogProvider.IOcProductStore,

How to solve?

Rename the 'ProductStore' folder (e.g. add '_old' to the folder name). 

Default directory of the 'Product Store' is 'C:\ProgramData\Knx\Ets6\ProductStore'.

In case you cannot find this folder, it may be because it is hidden. See here to read how to make it visible.

Then, start ETS again.