Based on the shape then either your AV software is in the way, or something odd contention/throttling going on.
Ookla reporting higher is no surprise based on the shape. The hint that something is up is the way the single and multiple download are a long way apart, and suggests each download is throttled to around 25 Mbps, and thus ookla who use a higher number of simultaneous downloads is also likely to report higher.
We can up the number of downloads, but that makes the test less reflective of actual use.
How is the connection behaving when you download a single file without any download managers/accelerators?