NCSI troubleshoot

Case: Windows 10 (virtual on vmware, virtual on Citrix, physical on laptops) have issues with NCSI test. Some of them. Below 10% of the whole number of hosts - total is above 10 thousands. Most of laptops work remotely (vpn), virtual machines of course should be treated like local machines.
Additional info: Windows 7 work perfectly.
Signs of problem: Citrix machines (virtual Windows 10) connectivity issues when staring Office 365 apps (no Internet connectivity on network status), after ipconfig /renew Internet connectivity is recognized well. For Windows 10 on virtual machines on VMWare and on laptops the only sign is huge number of requests to connecttest.txt on www.msftconnecttest.com per day. If workstation is working well - daily number of requests is below 10, if something is wrong is above 2-3 thousands. So if You multiply number of requests per workstation by number of wrong workstations there are above 400 thousands requests daily.

Steps to recover, to repair:
- dns record www.msftconnecttest.com is masked in internal - corporate DNS; no help
- www.msftconnecttest.com site is proxied locally in corporate server; it should be delivered better, but it's not; from this site I know exact number of requests no help
- UseGlobalDNS set to 1 no help
- disable offload for tcp/ip v4 - yes, it helped
- corrected manual entry of proxy - it is now recognized by system - visible in eventlog for ncsi

Important: only 10% of total number of hosts have this issue - all of them have the same set of patches, configuration, network configuration, firewall, antivirus and so on, so why only small fraction have this issue? I don't have a clue.