Well the problem remains with the latest firmware. I tried the NFS probe function also this time - nothing changed. Here is the output from the NFS diagnose function:
rw,relatime,vers=3,rsize=32768,wsize=32768,namlen=255,hard,nolock,proto=udp,port=65535,timeo=7,retrans=3,sec=sys,mountport=65535,mountproto=,addr=192.168.178.20
I can't see anything suspicious but maybe you guys can compare it to your output and see if there is a difference.
Tomorrow i will set up a samba share and see if that works. But i would rather stick with NFS if possible.
Thank you!