What you're describing sounds like the battery contact solder joint to the rest of the board is failing. The next time you have the issue, press and hold the button while looking in the "IR" window to see if you see a little red led flash. If not and it has new batteries, chances are good that's the issue. The bad news is you can't fix it without cracking open the fob but the good news is it's a great chance to fix everything if the fob is worn out.

Take care