1. A method of diagnosing transient down-layer performance problems using virtual-meeting performance data, comprising, by a computer system: generating a time-based performance pattern of a plurality of virtual meetings of a communications platform executing in a computing environment, wherein the computing environment comprises a plurality of down-layer infrastructural resources that support meeting services of the communications platform and non-meeting services of other components of the computing environment; determining, from the time-based performance pattern, at least one virtual-meeting attribute associated with relatively poor virtual-meeting performance as indicated by measured media-stream quality for the plurality of virtual meetings; identifying virtual meetings, of the plurality of virtual meetings of the time-based performance pattern, that have the at least one virtual-meeting attribute associated with relatively poor virtual-meeting performance; correlating, based at least partly on stored metadata, at least a subset of the identified virtual meetings to a particular down-layer infrastructural resource, of the plurality of down-layer infrastructural resources, that is at least partially responsible for executing each virtual meeting of the at least a subset; examining a performance metric of the correlated at least a subset of virtual meetings that is illustrative of an infrastructural problem which is broader than the communications platform; identifying a transient down-layer performance problem related to the particular down-layer infrastructural resource responsive to the examined performance metric satisfying a threshold; and reporting the transient down-layer performance problem.