I have encountered a situation where all GPO are applied for some user accounts, but only critical GPO get applied for other users because slow link was detected.
Our offices are on different coasts and connected via VPN tunnel. Until local server is available at each office, one of the offices is connecting to other for files, domain controller, etc. The link between offices is 10Mbps with 120ms ping.
I have already disabled slow link detection for workstations that seems to have this issues by configuring group policy slow link detection and setting it to 0 (Computer Configuration\Policies\Administrative Templates\System\Group Policy\Configure Group Policy slow link detection). Doing so does not help even after running gpupdate /force.
Shared namespaces are not available either and appear to be in offline mode. However, shares from each server in remote office can be accessed when avoiding namespace. On the other hand, dfs namespace through network mapped drive (policy applied) can be accessed with no issues.
Workstation: Windows 10 (also tried Windows 8/8.1) Server: Windows Server 2012 R2 Ethernet: OpenVPN Tunnel between two offices 10Mbps ~120ms ping
Disabling this policy will result in a default configuration. Any connection slower then 500 kilobits per second will be considered a slow connection.
To mark every connection as fast, re-enable the policy and set the Connection speed option to 0
Edit: Did you try to enable Do not detect slow network connections at Computer Configuration\Administrative Templates\System\User Profiles