After dropping everything down to the it is now my cpu issue is in the low 30s. Before was with 264 and 8192 on the 4mp cameras.Generally 8192 as the minimum for mine (CBR, H.264). Some higher where I want better quality for wildlife. Very noticeable deterioration in quality as it gets lower (e.g., grass starts sparkling and moving) . But if your priority is lowest resource requirements, then 2048 and H.265 will do that.
Your CPU % seems very high for 8 4MP and 2 MP especially if you're running at such low rates and using substreams. I ran the same I5-4570 for a long time. Might have hit that 50/70% before substreams were available but should be much lower now. Are you sure that the other cams actually are using the substream?
What happens to let you know that the substream on this one isn't working? No display in multi-cam views or it just shows the main stream?
Here's the error I get. This is just from changing the single / to the full string for the main stream. Same thing happens if I only do the substream.