I found a solution. Maybe this helps someone else with the same problem, too. It looks like some folders are in a weird state between read/write and read only. Mouse over the folder shows "Read & Write Standard Folder"Options menu shows "Copy Read Only key" but not "Copy Read & Write key"In preferences "Overwrite any changed files" is enabled. This should be only with read only folders I don't know why this happened, maybe from the update from 1.4 to 2.x. I have never used read only folders. So I deleted all the syncing on all devices and added all the folders completely new with new read write key. It was a lot of work but now everything seems woking fine like before.