We started getting this error on an SSL site running Umbraco 7.7.7 and the issue continues after an upgrade to 7.7.13. The site is hosted on a Windows Server 2012 R2 VM.

This is a similar issue to U4-9873 and 417 Missing token suddenly occurring on all our sites​ except an F5, or more thorough "Empty Cache and Hard Reload", fails to resolve the 417 errors.

When first login to backoffice, none of the Umbraco cookies load (UMB-XSRF-TOKEN, UMB-XSRF-V, UMB_UCONTEXT). An F5 causes the cookies to load.

Failed calls are to GetCheck, GetDashboard?section=content, and GetSections. Fiddler reveals the X-UMB-XSRF-TOKEN header is missing from these calls.

I have attempted a number of fixes from the Forum without success:

• set umbracoUseSsl to true or false - makes no difference
• delete all ClientDependency entries from \App_Data\TEMP\ClientDependency
• Removed Windows Update KB4014604
• I can find no evidence of custom/obsolete cookie issues as noted in Persistant 417 Missing Token Error
• no use of Application_PostAuthorizeRequest as noted in 417 Errors backoffice
• not fixed by any of the suggestions in 417 Missing token in the backoffice

I have not yet attempted these Forum suggestions:

• Uninstall .NET Framework 4.7 and 4.7.1
• Create a custom Umbraco.dll (from 417 Missing token suddenly occurring on all our sites​)
• Umbraco upgrade to latest, currently 7.10.1

Wondering if anyone else has encountered or resolved my particular flavour of these 417 backoffice problems?