We recently rolled out lightning and anytime Classic UI or Visualforce Page is loaded in Lightning Experience, that part of the page does not load. This affects standard pages such as the ones found in Setup as well as Visualforce pages embedded in Lightning Record pages. This affects only 2 users in all browsers. Salesforce IT won't help us because they say this is a Single Sign-on issue and is not covered for 'standard customers'.

The error in Chrome's developer console says: 

• Refused to Display: ..okta/com/app/salesforce/... in a frame because it set 'X-Frame-Options' to 'sameorgin'

I understand that the error means the same orgin flag was set in the reponse header, but I don't know how to fix it since this is standard Salesforce embedding (iframe) functionality.  Note, clickjack protection has been turned off.

Has anyone run into this issue?