I keep getting a small black box popping up saying 'refreshing sim data'. It doesn't seem to matter if I'm on my home WiFi, works WiFi, or using data. In some cases when gaming it has actually stopped the connection with the games server and so has dropped me out of the online game.
I had this same thing soon after getting the phone (would pop up 5+ times a day) which was improved when I was sent a new sim (saw it as about once every 2-3 weeks at most) . But it is now happening 5+ times a day again.