The current implementation of ScopeManager uses a ConditionalWeakTable to associate an Activity to a SpanShim. However, if the Activity used by the shim is not being sampled the associated Activity will be the singleton TelemetrySpan.NoopInstance and the Add method on ConditionalWeakTable will throw an exception. Repro test: 57845b2#diff-64d0dfb854bfa159bf2bfd49d7349af30848d52f4b9147e47e423b1e2d3399adL31