Slow Internet despite LAN cable (1 Gb line)?

A friend has a 1 Gb line and connected his ps4 to his router using a LAN cable. The router (info page from the router) shows that 1 gbit / s is arriving at its ps4, but on its ps4 this is only about 40 mbit / s arriving.

Can someone help?

Then limit the download servers.

If there are other cables along the course of the cable (SAT cable, power cable etc.), that could explain the slow Internet. Even with high shielding (CAT-6,7 etc.) power cables etc. Can interfere with the LAN cable.

How is the bandwidth measured on the PS4? And is that maybe 40Mb / s? Then that is very likely the limit of the available bandwidth of the download server.