MiniProfiler 3 affects on how TransactionScope and SynchronizationContext flow when ProfiledDbConnection, AsyncPump, ConfigureAwait(false) are used. I managed to reproduce the behavior difference in MiniProfilerReproductionTests.
MiniProfiler 4 does not have such side effect and works as expected.
My suggestion would be to upgrade to MiniProfiler v4 for anyone doing async :) (or in generally really)
In short: v3 was not very async friendly, breaks or behaves oddly in a variety of ways around it (e.g. "what is the root timing?", and will not be getting any further updates. A lot of how it handled things necessitated a rewrite of the fundamentals to be async friendly, which happened in v4. If you're hitting this, please update!