Win10 + Office 365 - Certificate Error for Certain Users. Diagnostic checking - receiving a certificate error message. https://diagnostics.outlook.com/#/:: This diagnosis produces the same ssl cert validation error also for users where all works perfectly.
Found the below article about maybe the same problem and possible fix, but can not understand what it means.
https://answers.microsoft.com/en-us/msoffice/forum/msoffice_outlook-mso_win10-mso_o365b/security-alert-outlookoffice365com/0392ddb0-30c1-4fbe-a104-d939e2da8e96?page=2