We have deployed a fix for this issue. Customers should now be able to set workspace execution modes successfully in the web interface as well as via the API.
Posted Aug 12, 2020 - 14:42 UTC
We are currently investigating an issue where customers may be unable to set workspace execution mode in Terraform Cloud via the web interface. The API for this feature is still functional and can be used while we investigate. Please contact the support team if you need further assistance with this feature.