Itunes Radio stops time out

Can someone tell me why itunes radio stops playback after about 20 minutes? This has gone on for months.

My internet connection seems fine to play the stream, but after a few songs it just stops. I can go back to itunes and click the play icon again to get another few songs.

I'm confused as I have a good internet connection, am using my computer when this happens (so not a computer time out due to no use), and I am a subscriber to their new $15/month music subscription. I can repeat songs and do a lot of that other jazz, but unlike pandora, my premium membership doesn't help with the time outs. Kinda *****...