If an admin enables clickjack protection for a customer's Visualforce pages with standard headers disabled, Field Service Visualforce pages will display a blank page or an error referencing content failing to load due to a CSP blockage. This occurs with the map view of the Gantt and when trying to view the Health Check page. Issues are also reported when viewing calendars and skills on the service resource record. 

Please note that clickjack settings can be enabled manually from the setup pages or auto-enabled on the results screen of the Salesforce health check utility under security. 

Why are certain pages loading completely blank?

To return Field Service Visualforce pages to normal, disable clickjack protection for customer Visualforce pages with headers disabled. 

1. Select the gear icon in the upper right-hand corner of the screen and select Setup.
2. In the quick find on the left, enter Session Settings.
3. Once session settings are selected, navigate to Enable clickjack protection for customer Visualforce pages with headers disabled and deselect the check box.
4. Select Save. 

The content will now be displayed correctly.

OR

A possible workaround to allow Visualforce pages to still display when clickjack protection is enabled:

1. Navigate to Salesforce Setup >> in the Quick Find search for Session Settings and select it.
2. Verify that Enable clickjack protection for customer Visualforce pages is selected under the Clickjack Protection section.
3. In the Trusted Domains section, click on Add Domain.
4. Enter your Salesforce org's domain (the URL you use to log in).  For example: <my domain name>.lightning.force.com
5. Select Visualforce Pages as the iFrame Type.
6. Click Save.