Today I was driving with cruise control on, and came up behind a slow car so braked, which caused the cruise control to deactivate as per normal.
However, after I had passed the car, I pressed resume, only to find that the cruise control had turned completely off (i.e. no light on dash).
I pressed the I/O button on the steering wheel to turn it back on, and the light came on for a second but then immediately turned off again. I tried several more times, but it kept just turning off. No warnings on the dash either.

Next time I started the car, cruise control is working perfectly again.

This is the second time this has happened to me in about 3 weeks. Does anyone know what could be causing this?