I don't agree with you. Your answer makes no sense.
Why does it work properly when I have an internet connection but goes really slow when there is no internet connection. I am not doing anything different. I am repeating the same steps. With an internet connection there are no issues. Take away the internet connection and the issues are present.
Where would these files be stored? They have to be stored to the local hard drive in the Volumes directory. Being local, I would think the file access would be no different than any other folder on the Mac.
@Joe11 I'm able to reproduce the Finder Preview long delay by disabling internet connectivity. But once Finder is able to repopulate the Preview Cache based on the offline files, all preview sequences in [Columns] view mode returns to normal operation.
There's potential for further performance optimization between Finder and Desktop App. I highly recommend contacting our Support Team at email@example.com to have one of our Support Representatives open an Engineering escalation on your behalf.