I received mine (UK) today and the remote was very problematic from the start, it would not register key presses, and then suddenly register them all at once, causing the cursor to fly around the UI. After an hour or so of messing around I've found that I have to be sitting in the right position on the sofa and hold the remote above my head for it to work reliably. Presumably I must have some interference on the BT frequency, which I believe is 2.4Ghz. What could be causing this?
Have you tried removing the batteries for a few minutes? Factory reset of the Chromecast?