Can you go to Internet normally? It seems there is a lot wireless interference.

Yes, the network is working well. I got ~27MB/s throughput using samba (udp protocol).

Paketloss only happens when RE450 has to route packets, also my ssh (tcp) sessions are stucked every few seconds for a few seconds.

Network setup as follows:
router -> (5GHz wifi 2,5meters distance) -> RE450 -> Cable -> server

ping from 10.0.0.1(router) to 10.0.0.2 (RE450) -> 0 Paketloss
ping from 10.0.0.3(server) to 10.0.0.2 (RE450) -> 0 Paketloss
ping from 10.0.0.1 to 10.0.0.3 -> 44% Paketloss

I got an additional issue, RE450 is unable to handle ipv6 - that sucks in 2016!!!

I am currently waiting for a dev of LEDE-project.org to build a firmware fitting RE450. My router is already running LEDE, I thought I can use the RE450 with stock firmware, too bad.

Cheers