Microsoft issued a warning that one of its new security updates may mess up your network file share connections. The software giant made corrections to how Windows enforces permissions, and one of the side effects of this is that users may find that shares devices like NAS systems may no longer be listed in the home network folder, and that previously mapped network drives are unavailable.
To fix this issue, Microsoft says you should change your network to "private" or "enterprise". As the Register reports, this security update is part of Preview Build 14936 and was rolled out exclusively to Windows Insiders, but it's likely it will become part of the general release in the future:
It seems that the cause of this hiccup is a fix that Microsoft made earlier in September to address a security hole severe enough that it might allow remote code execution with elevated permissions on an affected system, although this would require an attacker to create a specially crafted request.
The fix addresses this by, among other things, “correcting how Windows enforces permissions”.
Windows Insiders are typically no newbies and used to preview builds breaking stuff, but it is likely that this change will find its way into the Windows 10 code everybody else is running sooner or later.