I have the same problem. I'm pretty sure that it's a bug with how BI calcluates / probes CPU usage.
I have BI (and nothing but BI) running on an dedicated server - Dell R210 II, Windows Server 2016 Datacenter, Xeon E3-1280 V2 @ 3.6GHz (4 physical cores, 8 logical). 16GB of mem.
At present, the server has two 1GBps NICs bonded into an LACP team connected to a Catalyst 3560G. The box is servicing (at present) eight 5MP IP cams set at H265 / 1080P & 15 fps. They all connect to a Catalyst 3560-8 which further connects via gigabit fiber to to the same 3560G that the server lives on. Bottom line - overpowered box for what it's doing and a ton more network bandwidth than the cameras can possibly fill up.
The BI box is doing direct to disk recording / no reencoding.
I just checked, and BI was reporting 57% CPU usage. Task Manager reports 25%, and the cores are running at less than half of maximum frequency (44%), while Resource Monitor says that BI is 50%.
What I think that this means:
Resource Monitor is reporting that BI comprises 50% of all CPU usage in that snapshot. It doesn't represent processor load, but instead what percentage of active load a given process represents.
Short version: the processor group is actually running at 25%, and at less than half of maximum speed (SpeedStep slows the cores down when the additional horsepower isn't needed), and BI represents 50% of that 25% load. That calculates to BI itself causing a 12.5% load on the processors.
BI is reporting the percentage of processor load that is is causing, not the actual percentage of processor load. I would go with the Task Manager numbers ignore the percentage displayed by BI. IMO it's meaningless.