Instant Hotspot fails more than half the time between my 6s+ and 2013 rMBP (Sierra). And to get the WiFi hotspot to work you have to have the setting app open to the hotspot page.
This may seem stupid, but do you use it when both devices haven't been connected to the internet recently? Seems like it works better if the laptop was recently able to access your iCloud account.
This may seem stupid, but do you use it when both devices haven't been connected to the internet recently? Seems like it works better if the laptop was recently able to access your iCloud account.