This is more of a PSA than anything else...Fresh install of Ubuntu 20.04 plugged into the same firewall as another server running Ubuntu 18.04. 18.04 was able to upload at 22.894M/s, while the 20.04 server was struggling @ 1.8M/s. Poked around before I eventually realized I had enabled bbr flow control on the 18.04 server when I built it (https://www.techrepublic.com/article/how-to-enable-tcp-bbr-to-improve-network-speed-on-linux/). Did the same to the 20.04 server...and viola!
The latency will usually be more stable or even lower with BBR. Hoewever there are some downsides to it. Yes you get higher speeds in most cases. But the congestion control algorithm is not loss-based resulting in retransmitting 10-100x more than usual algorithms. The biggest discussion about BBR however is its fairness. BBR only works that well because not that many server are using it. It will slow down those with another algorithm (CUBIC is the default for major unix based distros and systems also android). There have been researches on it showing and proofing that in a mobile network BBR can claim basically up to 100% of the whole link bandwidth.
Also there are some specific use cases where you should avoid to use BBR. It's still relatively young and google is already working on BBRv2.
Regarding the OP. Your issue lies somewhere else you basically are taking the bandwidth with force
That's the thing - rclone copies are the only thing that show reduced network speeds without bbr (and quite frankly, I'm surprised it is such a speed increase). I'm not sure where else I would be having a problem, unless it was upstream with my ISP.
Unless...it was the fact that I had one server with bbr turned on (which does streaming outside of my network, so it is sending a lot) and that was causing issues with cubic/reno cca on the ubuntu 20.04 (as you said, using all the bandwidth)
John
Some data points - without BBR enabled, even directly connected to my ONT I'm only able to get ~1.8MBps with rclone while copying a 4GB image file. BBR enabled, and it's magically 10x better.
Trying from an oracle hosted VPS - regardless of BBR-ness, I'm seeing ~6MBps.