My Cloud Ulrta, But if I want to read data

My Cloud Ultra can record data very quickly, as I have described here. Therefore I copied large amounts of data with robocopy to the My Cloud Ultra and got ~120MB/s.
But if I want to read data, even with robocopy, then I only get max. 3 MB/s !?

I’ve checked all settings, provided each switch with the latest firmware and also checked the Windows 10 (1903) driver settings.
I just can’t find any errors!

Does anyone have an idea what this can be?

PC <--> GS108T Switch <--> GS108T Switch <--> FritzBox
		 WD MyClud Ultra Ex2 


Greetings from Berlin