Assume that you update your installation of Microsoft SQL Server Analysis Services (SSAS) 2016 to Microsoft SSAS 2017. When you synchronize a database in SSAS 2017, the synchronization takes a long time (about two hours) to finish. The same operation in SSAS 2016 takes only about 10 minutes to finish.
To work around this problem, set the EnableDisklessTMImageSave property to 0 in the Msmdsrv.ini file (in the /OLAP/Config folder) for both the source and target servers.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.