After seeing that my wireless speeds were much faster than the speeds I was getting over Ethernet, I decided to invest in some new cables. I didn’t know it before, but I saw while I was changing them out that my current cables were Cat 5e. While putting my network together, I had just been grabbing whatever cables I could find in my scrap drawers. Now I have Cat 8 cables and my speeds jumped from 7MB/s to an average of over 40MB/s. It’s a much bigger improvement than I expected, especially for such a small investment.
It’s highly likely that you had one or more bad-but-not-dead cables (like a weak termination) that was limiting your speed. By swapping everything out you fixed the problem. Cat 5e to 8 definitely shouldn’t have caused that much if a jump (if any).