K8090 sometimes wrong relais are switched

Hello,

I use the SK11 on the k8090, I linked buttons to it. but sometimes when I press the button of the 4th relais, it switches number 1,2 and 3 on but not 4. Sometimes only 3. And the problem only occurs after some hours of inactivity, then only one or two times.

Can someone think of a reason that might cause this? The wires between the k8090 and the button is about 7 meter.