I’ve had very bad luck with raspberry Pi’s and SDCards. They just don’t seem to last very long. I swapped to usb storage and things got somewhat better. I just had a usb drive die after 3 to 4 years of use. When I was still using SD it seemed like multiple times a year. Heat. Power loss, you can only punch holes in silicon so many times before it wears out. Whatever the reason.
My approach for this is configuration backup not the entire os. I think this approach is better for when it’s time to upgrade the os or migrate to a new system.
For my basic Pi running WireGuard and DNS, I keep an archive of documentation on steps to reconfigure the system after a total loss. Static configs are backed up once, and If there are critical configuration items that change then I back those up weekly. I’ve got two systems (media related servers, not Pi’s) that I keep ansible playbooks to configure 90% of the system from scratch so it’s as hands off as it can be.
Ethernet speeds historically were measured in 10/100. In my past life I worked for an a small rural isp. And part of my learning I was taught that cat5 was 8 strands of wire, or 4 twisted pairs. I got very familiar with crimping patch cables. If one strand were cut a network card would negotiate down to its lowest speed and still work at 10mbps. Operating on 4 wire or two pairs. It’s possible with those numbers you had a bad connection, or a broken strand in the cable and it auto negotiated down to 10mbps. To this day I still crimp my own cables, and I own a cheap cable tester to make sure the crimps and cables are good.