This was a terrible problem when I had a Lumia 920 on WP8.0 but not anything I've had a problem with on my 1520 unto just recently. I have a few tiles now that seem to be stuck on old content. One of them is the WP Central app.
I know it used to be that the live tile would stop after a few weeks of never opening an app. To get it to work again you just had to open the app. could this be the issue?