The loss did occur on simple ping commands, only on 2 out of 5 ports. The vendor confirmed the behavior to be faulty and took the switch back.

Maybe it was just a faulty model? However I do use multicast in my network (corosync) and a lot of 10G switches seem to have problems with that, maybe this was the case here, too.

The exact model is TRENDnet 5-Port 10G Switch, 5 x 10G RJ-45-Ports and there sure seem to be quite some people having issues as well…