Your long-term stats show about 1 Mbit/sec and your short-term about 3 Mbit/sec, neither of which are 10 Mbit/sec (which is usually an unrealistic best-case measurement using multiple threads, often to nearby).
Next step is for you to search for a speed limiter which might be things like disk, RAM, CPU, network, etc. Perhaps something will be found. Perhaps nothing specific will be found. Specific reasons require data…
What OS is this? Windows has some tools, Linux tools vary, and I’m not at all familiar with macOS tools.
What cloud are you going to, and how far away is the datacenter? Latency can be important to the speed.
You can also try to see what very-short-term network speeds look like via Windows Task Manager, e.g. in graph of some Ethernet or Wi-Fi adapter. The goal is to have a fairly smooth upload at maximum line rate. Large gaps or extremely erratic upload rates (assuming nothing else on system is uploading) may be bad.
Logging can provide quite a lot of information, but tradeoff is big output. One compromise level would be a live log view at About --> Show log --> Live --> Retry which should show files going up, and maybe retries. The best (very long) log is at Profiling level, but it’s probably too much to read live rather than with a log file.
The backup log also makes a “BackendStatistics” “RetryAttempts” number, but it only arrives after backup. Generally the initial backup (is this that?) is best done as increments, and that also eases debug of issues.