On my My Cloud app (iOS 9.2) I do not obtain any thumbnails for my photos. If I search for something I get the message “An diesem ort gibt es bereits eine Datei, oder es wurde ein ungültiger Vorgang versucht’” (sorry, I do not know the English equivalent).
I can still download pictures but if the picture does not have a clear name it is useless without thumbnails.
Strange things happen all the time with computers (this includes mobile devices). Get used to it. You did the right thing – “Turn it off and turn it on”.
BTW, you can use the internet browser to translate anything! Here is the German translation: ’ At this place there is already a file, or it’s an invalid operation was attempted ’ Not a great translation, but it gets the point across anyway.
Last night the Netflix app on my iPad would not turn on and connect. I deleted and re-installed app, and all is well again. Go figure.