Tested my slowly growing database in Nimbus Note with the iOS app, on iPad Pro 9.7", iOS 10.x.
After second synchronization, everything was there, including the structure of my folders and subfolders. After browsing a little bit in my base, suddenly the folder structure reverted to a previous version (ie the subfolders in my folders did'nt show). Interrestingly, all the notes were there, just not in there corresponding folder / subfolder.
I checked the web-version of Nimbus, fearing that somehow problem was transfered from the iPad version to the web-version: Fortunately, everything is fine there.
So I believe there is a bug in the iOS version. Happy to provide additional info if needed. iOS version of Nimbus Note was the one from 4-5 days ago; no updates shown in the AppStore.
Customer support service by UserEcho