SuiteCRM 7.11.18 Sugar Version 6.5.25 Build 344
PHP Version 7.3 / MySQL 5.7.35
When composing an email from the EMAIL module, selecting a template successfully inserts the template content into the email body, so it appears that the templates are correctly configured.
However, when any user (even system admins) click the “Compose Email” action on the “Activities dropdown” in the resulting pop-up for “Compose Email” when a Template is selected, the Body is not populated with the template.
This has been confirmed in the Accounts, Leads, Quotes, Opportunities, and Cases modules with multiple system users.