After a day of troubleshooting, a seemingly unrelated solution seemes to have solved both my mobile hotspot issues, but also the high CPU issues related to the ICS and BFE service processes that I was also having issues with along with this.
I didn't figure this out--just been hunting around and found an answer that I wanted to get back here as it looks like the same thing. See this thread for details: https://answers.microsoft.com/en-us/windows/forum/windows\_10-performance-winpc/after-update-to-version-1709-internet-connection/ab68fb4c-a1b8-4ec3-aa18-32a104e21172?auth=1
The basic summary is that resetting the Windows Defender Firewall to the default settings resolved the issue.
To do this open
Settings -> Update and Security -> Windows Defender -> Open Windows Defender Security Center -> Firewall and Network Protection -> Restore Firewall default settings
Hope this helps and works for someone else... Seems like a fairly widespread issue.