Utilizing the listed options for adding a new CloudSOC Securlet for monitoring CASB Applications 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 list of apps.
At that time of earlier releases of prior DLP versions, some Securlets that were due to be implemented were in fact not included in the integration with DLP.
For example, where there are Gatelets for Facebook Workplace, for example, they are not currently supported as Securlets for integration with the DLP Cloud Services.
E.g., 15.8 list shows Cisco Spark, Dropbox, SAP, and Yammer:
15.7 list shows above plus Facebook Workplace and Workday:
Remove any unsupported apps, then re-click the "Cloud Sync" option in the UI.
To see a list of currently supported Securlets in the CloudSOC, please see this Help Center topic: