Take a copy of your sketch and disable parts of the functionality until you find which part causes the problem. For example, you could take out anything that tries to interact with the RF24 hardware and see if that helps. Once you know what is triggering the problem, you will probably be able to guess why it's doing it.
Any special reason why you're running it with the RF24 disconnected? I suppose that it's possible that whatever-it-is will be corrected by adding the hardware the sketch is expecting.