I reached out to Sugar Support and apparently it's a bug they don't yet have a fix for. They recommended that I reach out to the community to see if a customization can be created to address this issue.
Steps to reproduce:
1. In Studio, create a custom field in Calls module called "Test"
2. Add the field to the Calls Record View layout.
3. Save and Deploy.
4. Go to the Calls listview
5. Click the preview icon to view the call record in the intelligence pane.
Expected Result: You see the custom Test field in the preview.
Actual Result: You do not see the custom Test field in the preview.
This happens for both the Calls and Meetings module.