For years already I got a problem regarding download speeds and I isolated this behavior to something Windows 10 related. First of all I have a 1Gbit connection which works fine. I am getting <130MB/s normally.
Now something burned into my settings that I am not getting the full speed. Sometimes I am getting 100MB/s and more but only for short. Average is around 80. Sometimes even less. This came years ago. Like 5 or more years and I never found a solution. The last time I took care of this I was very sure it's something in Windows because I installed it on my Laptop and logged into my Microsoft account. Boom that made the Laptop doing the same. Today I did a fresh Windows 11 install to test Windows 11 and download speed. I did not connect Microsoft account and download is fine at stable 130MB/s.
Now the question... what in hell can be a cause for this. As I said I tried for years fixing this but always came back. I also removed all deviced from the Microsoft account and did a fresh install. This was around 2-3 years ago but it came back. Also before I had 1Gbit the problem was the same but with slower speeds. At 500Mbit I struggled around 10-40MB/s and lets not talk about 100Mbit.