Utilizing the listed options for adding a new Elastica Securlet for monitoring in the DLP Enforce UI, you find that it is not completing its "sync" successfully.
"Sync Failure" shows up when the "Sync to CloudSOC" operation completes.
There are a few Securlets which were NOT supported for Application Detection, despite being included in the v15.0-15.5 list of apps.
At that time of earlier releases of the 15.0-15.5 GA, the following Securlet was in "Beta" in Elastica CloudSOC - and therefore invalid for DLP Cloud Service integration:
As of 15.7 however, Facebook Workplace is a valid Securlet.
Currently, the following is still not a valid Securlet (as of December 2020):
While there is a Gatelet for Microsoft Teams, it is not currently supported for DLP detection.
Remove any unsupported apps, then re-click the "Cloud Sync" option in the UI.
FYI - although the Cloud Detection Server cannot monitor "MS Teams" activity via that Securlet, content shared via the application is picked up via O365 Securlet, where the file is shared via a path in SharePoint.