How to fix packet loss when connecting directly to a piece of hardware?

Question

linux

Configuration: laptop + piece of iron performing network operations - Rbox630.
When connecting a laptop to a piece of iron through a router, the ping goes without packet loss.
When we connect directly 80% of the packets do not reach the piece of iron.
How can the cause be diagnosed?
Wireshark says there is no response from the host (hardware).
Static IP is set. routes are written.

Answer 1

I look at the characteristics, it has 2 network ports, one gigabit another 100Mbps, suddenly when you connected directly you plugged a port into 100Mbps and for some reason he wanted to work in gigabit mode (although then nothing would work at all)
Also, check in which mode a piece of iron is connected, suddenly, when connected through a router, it gets up to 100Mbps or half-duplex, and when connected directly, it tries to connect at maximum speed and the speed of the iron is not enough to process or some other cant.

Answer 2

The first thing that suggests itself is that the cable is directly too long, crimped and / or of poor quality, and through the router this distance is divided into two pieces, plus perhaps better cables.