Ethernet speed problem

Hello
I am using rockpi 4c with android 10 .sometimes ethernet speed is being so slow (ftp upload speed is being 50mb/second to 10mb/second) when I restart this system .ftp upload speed is beginning again 50mb/second. how to solve this problem without system restart?

thank you for your help

Low hanging fruits: replace Ethernet cable, try again.

Always check from bottom to top.