i figured out the problem. it has something to do with 10Gbe network cards, but i dont know where to search, or how to investigate that.
i made a tcpdump but everything looks good
pbs connection 1Gbe to 1Gbe is fast
pbs connection 10Gbe to 1Gbe or 1Gbe to 10Gbe is slow max 2MB/s.
both servers...