I'll try to do the network test though.
Thank you for your help.
I thought you had meant that you literally replaced the network cable - removing the one you had from the miner and the switch/router and replacing it with another known working cable. You mean that you disconnected the cable from the plug on a good miner and plugged it into this miner? Right?
I was just reading another issue from another user that was having dropping issues - sometimes working for a while then not, etc... I know this isn't your particular issue, but maybe worth a look. Someone had posted that they were also having similar problems and ended up solving their problem by turning off IPv6 on their router. Possibly, their router was sometimes handing out an IPv6 address to the miners causing problems - or causing routing issues? Just something else to check - make sure your router only has IPv4 turned on and IPv6 is off. Just to make sure it's not an IPv6 issue.