Q: Connecting via USB version 12.3.3

Try restarting the AMDS >  Restart the Apple Mobile Device Service (AMDS) on Windows

i'm having the same issue, tried restarting the amds, but that didn't work.

iphone 6s plus - ios 9.3

itunes 12.3.3.17 (64 bit)

windows 10

Had the same problem.  Your Apple driver needs to be updated on Win10.

Found this on an Apple blog dealing with the same issue and it worked for me and my sister:

For  Windows Vista, Windows 7, or Windows 8, Windows 10

1. Go into Settings, Device Manager, View, Show hidden devices, Portable Devices
2. Right-click the Apple iPhone entry an choose Update Driver
3. Click "Browse my computer for driver software".
4. Click "Let me pick from a list of device drivers on my computer".
5. Click the Have Disk button. (If the Have
   Disk option is not present, choose a device category such as Mobile Phone or
   Storage Device if listed, and click next. The Have Disk button should then
   appear.)
6. In the "Install from Disk" dialog,
   click the Browse button.
7. Use this window to navigate to the
   following folder:
   
   C:\Program Files\Common Files\Apple\Mobile Device Support\Drivers.
8. Double-click the "usbaapl" file.
   (This file will be called "usbaapl64" if you have a 64-bit version of
   Windows. If you don't see "usbaapl64" here, or if there is no Drivers
   folder, look in C:\Program Files (x86)\Common Files\Apple\Mobile Device
   Support\Drivers. instead).
9. Click OK in the "Install from Disk" dialog.
10. Click Next and finish the driver-installation steps.
11. To ensure you have the latest version, once again go to Device Manager, View Hidden Devices,  this time go to Universal Serial Bus Controllers, Apple Mobile Device USB Controller– and then right click to update driver.  Let system find it.
12. We restarted our systems at this point, then went back into iTunes and connected our iphones. It worked!

We also did try to just update the drivers first but that didn't do anything. I'm hoping this more extensive driver update works for you. Let me know!

So glad! I hope others try it too. Looks like this new iTunes release has many problems.

Thank you for your help! it works on my 32-bit Windows 10 Pro.

Great news!

I too am having sync issues with both my 6S+ and my iPad Pro, as neither of them will sync to iTunes after the 9.3 update. I'm running Windows 10 64bit and can't get anything to work now. This will be the last update I do until I can see if anyone is having any issues with any new updates in the future.

Alternatively you can mark usbaapl64.inf within C:\Program Files (x86)\Common Files\Apple\Mobile Device

Support\Drivers and choose install from the context menu. Windows will install the driver immediately and open itunes showing the missed iphone.

This was incredibly helpful.  Thank you so much!

I've had 2 MAJOR issues with Windows 10 and iTunes... I'm not sure why it keeps happening.  I'm guessing that one side (or both sides) don't feel the need to work together and we get to suffer because of it. 

I am forever indebted to you. THANK YOU SO MUCH.