Constant rebuffering stream interruptions since 12.1.2.27 upgrade

Question

Home sharing appears broken since I upgraded to iTunes 12.1.2.27.  An old XP desktop manages my large Library, although the actual iTunes media folder is on an external hard drive.  I generally share to a Windows 7 laptop in another room and to an iPad.  Since loading 12.1.2.27 on both Windows computers, I rarely get to listen to a whole song before the sound stops and a Window pops up on the laptop titled "Opening URL" with the content "Rebuffering Stream".  If I don't click stop, this Window will persist forever.  (By the way, when this Window was up, I couldn't navigate to this site - once it was closed, no problem).  On clicking close, sometimes when I hit the play button again in iTunes, I restart the interrupted song.  Other times, a Window pops up saying Opening URL, but not Rebuffering Stream.  If I click stop on that window, generally the shuffle play list is regenerated with different songs, but again, the rebuffering stream window is very quick to return.
The Music player on the (latest iOS) iPad (which has no local content other than the unwelcome U2 album) is a little more robust, but is also (even more than usually), subject to sudden losses of audio, paging quickly through the songs on shuffle play without playing any of them, displaying the play or pause button randomly without a relationship to whether the song listed is paused or playing, and requiring the sometimes 20 to 30 minute process of reacquiring my shared library.  Again, it's a big library, > 230 GB.

Answer 1

Hello, bobzim.  
Thank you for visiting Apple Support Communities.  
Here are the best troubleshooting steps to go through when experiencing streaming issues with Home Sharing.  
4. Check your network connection
Home Sharing requires a home network with an active Internet connection. All the devices you want to use with Home Sharing need to be connected to your home network.
In addition, verify that:
All your devices are connected to the same router, if you have multiple routers. Using multiple routers may prevent discovery between these devices.
Your devices are not using a Virtual Private Network (VPN), or that they are all on the same VPN. A VPN may isolate the device and cause connectivity disruptions.
If you have a router set up with a guest network, make sure all devices are either connected to the guest network and devices on the guest network are allowed to communicate with each other, or switch all devices to the primary network on your router.
If your computer is asleep or shutdown, or iTunes is closed, there's no access to the shared iTunes library. Wake up or start the computer and open iTunes to regain access to that library.
Your router needs to be up-to-date. If you are using an AirPort or Time Capsule, learn about firmware updates. If you are using a router from another manufacturer, contact the manufacturer to inquire about available updates.
5. Check Firewall settings
If you have a firewall enabled in your router or computer, make sure that the firewall is not blocking communication between your computers. Home Sharing uses TCP port 3689 and UDP port 5353 to communicate with shared iTunes libraries.
In addition, Apple TV and Mac computers will use port 123 to set the time automatically. Incorrect date and time on either the computer or Apple TV can cause errors for Home Sharing and connections in general.
If you are unsure whether your router has a firewall or the required ports open, test additional devices or another network to help isolate the issue. If the devices tested work on another home network, it is your router or network configuration.
For Mac OS X, you don't have to edit the port addresses, but make sure the firewall in Apple () menu > System Preferences > Security > Firewall are not set to:
Block all incoming connections
Allow only essential services
If you use another security/firewall software on your computer or router, follow this article or contact the manufacturer or check the documentation on how to open TCP ports 123 and 3689 as well as UDP ports 123 and 5353.
For more information on ports used by Apple products, see Well known TCP and UDP ports used by Apple software products.
7. Restart your network router
Restart your home network router using the method recommended in documentation from the manufacturer. This may include disconnecting the power cord for thirty seconds or more.
Note: During this period, Internet services such as a VoIP-based phone will not work, and any additional routers may need to be reset in sequence.
Troubleshooting Home Sharing
Cheers, 
Jason H.