Assume that you install Microsoft SQL Server 2016 Analysis Services (SSAS 2016) or SSAS 2017 in multidimensional mode. When you process the dimensions by using the Process Update option, you may receive an error message that resembles the following:
Internal error: An unexpected exception occurred.
You may work around this issue by performing a Process Full operation before the Process Update operation. Because this issue only occurs when you perform the Process Update operation after the SSAS service is restarted.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.