If i'm not mistaken, the sihost.exe executable is responsible for rendering the native metro start bar. I'd assume that start10 is either interacting with it, or replacing it in which an actively busy sihost process is still indirectly affected by start10.
You seem to have mentioned two processes.
SVCHost.exe which is responsible for hosting some services and SIHost.exe. I assumed your mention of SIHost was a typo.
ShellExperienceHost is actually responsible for hosting the Windows 10 start menu and Start10 should never get pulled into this process. When you open the Start10 menu the original menu simply never gets asked to open.
Whilst Start10_64.dll may be pulled into SIHost.exe automatically, it does nothing whilst in that process. Start10 only functions inside the explorer process which is the process that provides the taskbar, desktop etc.
If you are experienced with Process Explorer it would be interesting to know what thread is using all that cpu. The original module which started the thread should be listed. It may be there is some conflict between Start10 and another application that is somehow causing a conflict but this is not normal and a check here is not showing a problem and we have no other reports of similar either.
I would also recommend an antivirus scan on your computer as viruses are known to impersonate other processes with common process names in order to be hidden.
