I've successfully loaded music on to my 8300, and it shows in the Media Player. But recently I loaded more music, and while it shows in the "Explore" option from the main media screen, it doesn't show in the "Music" view (and playlist, etc).

Anyone seen this, resolved this?

Did you format your card while in the device? If not you will need to in order for things to work right. All data on the card will be lost when you format so back up anything you need to keep.

I had the same problem, and it seemed to go away on it's own.
At first I only had the first couple albums I loaded being listed, but could find them using "Explore".

I believe once I just stayed in the "Artists" or "Albums" list for a few minutes, they slowly started to show up there. I think the Media Player Application may scan the media card while in these screens.

Hopefully someone can confirm this, or come up with a more comprehensive answer.

It does take a little while for the new music to show.