After activating the function

I am using nextcloud on a local linux installation with docker images. Current version 19.0.4.
I am using server-side encryption only for an for external storage. This is working.

After activating e2ee it seems that all is working. A local empty folder could be cerated, and I was able to mark it to be encrypted. When no file is in the folder, it seems to be ok.
After storing a file in the folder it seems to be ok locally. On the server the folder seems to be empty the whole time. After one or two syncs the local folder is empty again.

Does is have somethign to do with the serverm side encryption?