Probably the widespread traffic issue. Go to Settings → General → Traffic and disable traffic. If the framerate returns, you should be able to turn it back on again immediately and still have it back, but it will degrade over time again.
Probably the widespread traffic issue. Go to Settings → General → Traffic and disable traffic. If the framerate returns, you should be able to turn it back on again immediately and still have it back, but it will degrade over time again.