Same problem started to occur this autumn with my 2013 RX450h.
At first when I pressed the button it openeb, but didn't close - only two beeps.
Then after a few weeks it didn't open anymore from the remote button - only from the car - two beeps again when the remote button was pressed. And finally I heard only two beeps whenever I pressed a button.
Now it's starting to get warmer already and voila, one day I tried to press the button again and it worked - it opens and closes every time.
So my conclusion is that cold temperatures are the cause in my case. But now is the question - where is that weak point that gets affected by cold weather?