When reviewing the Enrollment Statistics, you can click a link from the 'Authentication Pending' count to see an Entity search filtered by that specific SEPM's clients in the status clicked.
There is a timeout set internally which this search may reach easily, due to the granularity of the search.
This is the expected behavior to prevent internal database damage and CPU over-utilization. The workaround is to perform this search as an Entity query using the provided filters: