Thanks for the quick answer. I did the upgrade, I am also using the same USB devices with excat the same files and have tried it in single and playback mode, but it makes no difference.
I guess using the footswitch input will always have some milliseconds of latency even if the devices are excact the same. There are too many random factors why both systems start differently.
Our show is not working with just I single playback device. It is necessary to have a backup device 🙁