For example a single machine using all the bandwidth, but you start opening web pages on that machine. Everything is slow. Opening a youtube video shows that I have like 1mbps for the video and the other task (steam download) is at 8mbps.
If I start the same video on a second device it gets like 4mbps, and steam download drops to 4mbps like it should.
It's even worse with torrents, the more connections the worse. To the point I can't even open a web page.
Only fix is to set flowblind, that gives gives fair bandwith between the downloads/uploads on a single machine, but causes higher latency spikes and it's worse when there's more devices on the network.
Edit: I figured it out, it's working properly now.