Dropbox Securlet does not report some activities or DLP policy violations. But the activity and violations are reported in DLP Enforce.
Note that Dropbox Securlet is not currently supported for customers that did not already have it enabled as of April 2020. This issue happens for customers that still have the Dropbox Securlet from prior to April 2020.
Please contact Broadcom support with the users that are affected. A script can be run that will resolve the issue for those users.
A permanent fix is being looked at by Broadcom Development