Given that Personal Hotspot has no API surface, this is more of a user-level question than an code-level question. You might have more luck asking it over in the Apple Support Communities, run by AppleCare.
We have not yet been able to connect one of the iOS devices up to a computer to gather the logs yet as this happens on devices we don't own or have immediate access to.
Just FYI, on iOS 10 devices you can grab a sysdiagnose at the time the problem occurs and then download that from the device at some time in the future. The Bug Reporting > Profiles and Logs has instructions for this. It also has instructions for grabbing more Wi-Fi diagnostics, which might help here.
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"