Hi all,
I found the cause and workaround solution for this case. If you received this error, the reason that you have some apps that size is too large (may be more than 3 GB size or something). At normal, such app should be file explorer or container or media player or some thing. Then, itune will show that iphone disconnected problem during backup. For my case that is related that my media player have around 50GB media files inside.
It cause this problem.
You have several workaround ways to resolve this issue.
Case 1. Don't use such app. remove it.
Case 2. Use such app and store the data into clouds and reduce local storage
Case 3. Some apps contain function not to perform backup through iTune. Enable such feature
Hope this work around can help you. In addition, this should be the bug in Apple iOS and iTune. Hope Apple will resolve this issue asap.