I had this when I got my Strix B550-F Gaming, and i guess the problem is still there. Don't know if it's a driver issue, as I updated drivers but it didn't help.
Instead it was a cable that didn't work (but worked on all other computers). I could fix it by changing the duplex in networks settings to 10 Mbit half duplex then back up to 100 Mbit full duplex again, but i had to do this manually every single reboot and even every single time after the conputer woke up after hibernation/sleep mode, so extremely frustrating.
But it only happened on certain ethernet cables that were not exactly the best, like very long ones from building the house 25 years ago... or very bad cables... but trying around still most cables work.... I've never had problems with these cables with any other computer so something is weird about the i225-V that makes it pickier about cables... simply won't recognize that a cable is even inserted if it is not good enough... if you have the option of using other better ethernet cables, try that it will almost certainly work. If you need to use those perticular cables, or if you have wall plugs that are somehow too bad for this oversensitive controller, i guess just buy a usb hub with ethernet. or a simple usb ethernet dongle...
But the main point is that for some reason it is way too picky about cables, "bad" cables (that aren't really bad and work fine for all other computers, routers and printers) won't even get recognized as bad cables but just as "no cable detected". I've found no solution, and I doubt drivers will ever solve this, it might be a hardware issue.
