I've spent two full days researching and trying different solutions on this.
Let me add a clearer way to see the problem:
I uninstalled and reinstalled MB. When asking if I want to scan my folders for MB library set up, it only shows a couple of folders on my C: drive. So I unchecked them. The same window however, also presents a box "choose folders".
Click "choose folders" and it shows:
_ Windows C:
_ WLAN backup hard drive
(Interesting that it shows the WiFi hard drive, but neither of the removable drives on my PC -- the SDXC card or the USB drive.) My music files are all on the SDXC card.
And then, this is probably the most helpful way to see the problem:
>I go into Edit/Preferences
>Under Preferences/Devices the SDXC card clearly shows as a device. (Note the "Folders" box at bottom of that window is empty.)
>Under Preferences/Library/Monitored folders there is another "choose folders" box. Click it to choose the SDXC device and the Music folder in it (with all my music files), but again, it only shows the same 3 folders as when I clicked it above. The SDXC does NOT show up as an option to choose music source files from -- even though it shows in Devices.
That's where I dead end. Can anyone else replicate this problem to see the issue?
Also, at https://getmusicbee.com/downloads/
it shows the May 6, 2017 version of MB is "MusicBee 3.0.6335; Released on May 6, 2017; For Vista/ Win7/ Win8/ Win10"
Doesn't show a 3.1 version. So 3.1 must be in Beta?