When you first bought your smart TV, its software — the streaming apps, user interface, and so on — probably felt pretty snappy and responsive. But if you’ve had your TV for more than a few years, I’d bet it’s starting to seem sluggish, if not downright temperamental. You click the remote to launch an app, and the TV just churns like it’s making up its mind. It’s frustrating when a once-zippy TV becomes slow or unreliable, making navigation tedious and causing streaming apps to crash. Here’s why it happens and what you can do about it.