The socket isn't supplying enough energy to keep the clock running at full momentum, you'll have to get in touch with your energy supplier and ask them to do a socket supply range check, might need calibrating.
Would you believe I was able to factory reset the alarm clock and it is now keeping the right time. Who knew that alarm clocks could be factory reset using a key combo!
How did you do It? I have the same clock and it loses time too (only a couple of minutes but still loses time)