I covered a bunch of Auto Import issues over in your other thread:
https://yabb.jriver.com/interact/index.php/topic,121292.msg838604.html#msg838604As you are seeing audio files not being imported, the issues covered in that thread are probably the issues here.
If I go and open the file(s) in question into JRiver manually they play fine.
How are you doing that, via Windows Explorer?
Because if you are going into, for example, the View "Video > Files" to find the files and play them, then the files are already imported into MC. Only imported files show in that View.
If the same files don't show up in the View "Video > Movies" or "Video > Shows", then it will be because the [Media Type] and/or [Media Sub Type] fields are wrong for the files, so they are not being included in the View.
If the files show in the "Video > Files" View, select one, open the tag window, and check those tags/fields. Fix them, as appropriate. You are new to MC, so search the Wiki for the terms [Media Type] and/or [Media Sub Type], follow some links, learn how MC uses tags/fields, Views/Smartlists/Playlists, the Expression and Search languages. Have a look through this area:
https://wiki.jriver.com/index.php/DevZoneAnother tool you can use to check if files have, in fact, been imported even though you can't find them is the Explorer inside MC. No, this is not Windows Explorer, and works very differently, though it will be familiar.
In the Navigation Pane on the left of MC, select "Drives & Devices > Explorer" then make sure the two check boxes at the top are selected, "Show files in subfolders" and "Show only files in Library". Then drill down into your "F:\Transfer" directory, and see what is shown in there. If you can see the "missing" files, they aren't missing, and MC has already imported them. If you can't see the missing files, untick the "Show only files in Library" checkbox. Do they now appear? If so, then the files are visible to MC, but have not been imported. Run Auto Import manually and they should appear in the Library. Check tags if necessary.
MC has a bit of a learning curve. You have started up that curve. Keep going. Read more. Use search in the forum and Wiki. Try the custom Google search at
https://www.jriver.com/support.html if you need better search capabilities.
The file(s) just wont appear in the list.
I have sort of covered it above, but which list are you looking in?