rsync and scp connection dies unless speed limit set

Hi all,

i am a medium skilled Linux user, running OMV on my Terramaster NAS for quite some time now (roughly 1 year).

Everything was fine with my NAS till now. All of a sudden i am not able to copy large files from my Linux laptop (Vanilla OS) to the NAS. No matter if i try to send files with rsync or scp or sftp, i can transfer a few MB and than the connection breaks with:

ETARead from remote host 192.168.2.10: Connection reset by peer
client_loop: send disconnect: Broken pipe

Having a ssh session open is also working fine.

The interesting part for me is: The problem is only when i copy from a remote host to the NAS. The other direction works fine

I could also limit the speed using

$> scp -l 8192 .... 

and in this case the transfer of 6GB file was successful but did last 1 hour

Anybody some ideas what to check and where to look for failures.