Hey,
i am new here, so sorry if I forget anything 
I have installed a new version of NC AIO. Next, I have activated the external storage app and connected bmy NAS shares with my NC over SMB (global credentials).
Now to my “problem”: If I create a new document in a external storage folder, I can open it normally and write. However, if I want to save the document, I get an popup with a error message saying: “you can’t save the document, check you permission”. I noticed that the popup is misleading, since the content is indeed saved correctly (reopen the file and the content is there). Since I can access all external storage folders without any issues, I guess the problem (permission etc.) is not there.
Note: If i create a document NOT on a external storage folder, I don’t get the popup.
Thank you very much!