In our testing before Windows 10 release, we found an issue with upgrade from Windows 7 to Windows 10. After the upgrade, the Work Folders partnership was not kept, as a result, sync will stop. User will need to go to Control panel, and setup the partnership again.
To address this issue, we released a QFE to Windows 7, so the Work Folders client can continue to sync after the upgrade.
The QFE download is here: https://support.microsoft.com/en-us/kb/3081954
If you are using Work Folders on Windows 7, it's important to install the QFE.