Cross and UmixPro disconnected while playing a set

Last sunday I made a "nice" experience. During my set the UmixPro was suddenly disconnected.
Cross 1.6 was still working but no button on the Umixpro (both players) did work anymore. I went on driving Cross with the mouse. Then I switched off and on the UmixPro and it worked again.
Strange.
I was working a lot of weekends for months with Cross and UmixPro. That never happened.
Any ideas what the reason was and how to avoid?

Cross 1.6 was still working but no button on the Umixpro (both players) did work anymore. I went on driving Cross with the mouse. Then I switched off and on the UmixPro and it worked again.
Strange.
I was working a lot of weekends for months with Cross and UmixPro. That never happened.
Any ideas what the reason was and how to avoid?
