After a reboot, machines disappear from the network. What can be wrong?

Question

linux

In general, the situation is like this. There is optics, a router is connected to it, an old laptop is connected to it with a cable as a home file washer (Ubuntu Server 14.04.5) and a PC (Xubuntu 16.04.1), the router also distributes WiFi. DHCP is enabled on the router. Everything works, but only until the first reboot of one of the machines connected via cable, i.e. if I reboot, for example, a file washer, then it is in no way visible from the PC (it does not ping, it does not connect via SSH, etc.,). However, if you switch to WiFi, then there are no such problems, everything pings, connects via SSH. What can be wrong ?

Answer 1

rt router?

Answer 2

connect by name or by ip? Do hosts have static IP or DHCP?

Answer 3

accidentally in a route not on a static ip it is entered? I mean, the cable and wifi have different poppy addresses, and ip, respectively?