This has been happening ever since Cyberduck was released. I am using v5.1 (20632)... update today... and still the same results. As a result I've not been able to upload large files or large amount of files in a meaningful timeframe. This is true even being at Backblaze's office on multi gigabit connection. Talking to our team there is no reason for the decrease on our side.
Attached are screenshots of this progressive decline in speed. The screenshot names contain time stamps.
Please contact Backblaze B2 support to look into your issue in-depth. We previously have seen this when they had an issue with their router configuration for requests from certain locations (AWS eu-west-1 region in this case).
Per my notes I am doing this from the Backblaze office (I am an employee) and have already run this by the engineers and support directly. They've explicitly stated this is a Cyberduck side issue.
Not only does the speed decrease, but each time an upload is paused the amount uploaded resets to a lower amount than what was reported upload the previous session. . For example it says 2GB have been uploaded and I pause the upload... the next time I start it will start from 300MB vs 2GB (the starting amount of my last start) or some partial amount (ex 1.2GB) but never the full amount uploaded on the last session. This has been like a Ground Hogs Day the movie for the past 2 months. I've been trying to upload the same 8.9GB folder over this duration with new builds and the same thing keeps happening.