CarPlay works sporadically with iPhone 6 and 2016 VW Jetta GLI

I'm having sporadic trouble with connecting my iPhone to the CarPlay system in my car, too, and I have tried almost literally every possible combination of troubleshooting and I'm still having issues.

Sometimes it connects just fine, other times it does not, and no matter how many combinations of the following I try, nothing will get it to work again in that session.

The gap between the times it works and the times it doesn't and the times it doesn't work again usually is as long as it takes to shut off the car, unplug the phone, leave and lock the car, then return anywhere from 10 minutes to 10 hours later. However, even when I try to duplicate that process in the span of 30 seconds, it doesn't connect.

It truly seems like it needs me to completely leave the car for some period of time before it will work again (or not), but that of course is patently illogical (unless there's some hidden issue I'm not seeing?)

Here are the details:

2016 VW Jetta GLI with CarPlay (MirrorLink)

Apple iPhone 6 (MODEL MG602LL/A)

iOS v10.2.1 (but this was happening before this latest update, so I don't think it's the ".1" security fix that's causing the problem)

Official certified Apple USB->Lightning cable purchased at Apple Store

I have tried virtually every combination of the following:

• Restarted the car
• Rebooted the iPhone
• Turned Siri on
• Started up the vehicle with the phone plugged in to USB while locked
• Started up the vehicle with the phone plugged in to USB while unlocked
• Started up the vehicle with the phone unplugged from USB. After startup, plugged it in to USB while locked
• Started up the vehicle with the phone unplugged from USB. After startup, plugged it in to USB while unlocked
• While the iPhone was plugged in and the car was on, unseated and reseated the USB cable in both the iPhone and the car
• Reset App-Connect to Factory Settings in Jetta's MMI: Settings > Factory Settings > App Connect
• Reset ALL Factory Settings in Jetta's MMI: Settings > Factory Settings
• In the iPhone Settings > General > CarPlay, selected "Forget This Car"
• In the iPhone Settings > General > CarPlay, turned on "allow while phone is locked" (sorry forgot the actual verbiage)
• In the iPhone Settings > General > CarPlay, turned off "allow while phone is locked" (sorry forgot the actual verbiage)
• When AppConnect/CarPlay is attempting to connect to the iPhone, a dialog box appears on the iPhone asking if I want to "allow" or "not now" connection while the phone is locked/unlocked. I've answered both "Allow" and "Not Now"
• In iPhone Settings > General > Restrictions, ensured Restrictions are ON and CarPlay is allowed
• In iPhone Settings > General > Restrictions, ensured Restrictions are OFF and all Apps including CarPlay are allowed
• No 3rd party VPN apps are running or installed on the iPhone