LattePanda 3 Network very slow or breaks with bigger files

I installed linux (Ubuntu 0423 and 1023) on LattePanda. Everything works fine except network over wlan or ethernet. 

Login is no problem, but transferring a bigger file to LattePanda aborts after a few seconds. Doesn't matter if scp, samba networt, nfs.

Also ssh connection somtimes has breaks.

The other direction: transfering from LattePanda to other computer is no problem.

Do you know that problem? What can I do?