I am running Evernote on Android 6 (Marshmallow) and elected to use my SD card as internal storage. I then had a problem with the SD card disconnecting from the system periodically, so that it appeared that the SD card had been unplugged. I seem to have fixed this by moving Evernote to the actual internal storage (instructions below). While this may seem to defeat the purpose of expanding effective storage, it does not, because other programs use the extended storage, leaving more for Evernote.
Here's what i did: I went to Settings, Storage & USB, Sandisk SD card, Apps. This brings up a list of apps that Android has moved to the SD card, If they are not sorted by size, you can sort them using the menu. I started moving some of the bigger apps back to internal memory by selecting them and clicking "Change."
Dan