The hierarchy now uses a request barrier after the first synchronous request completion. Async requests could occasionally complete fast enough that DispatchRequests would be left to handle the completion. In that scenario, there would not be a barrier in place when beginning any subsequent requests, which would lead to a failed assertion in the request owner.
#preflight 63ceb5c63a03cb0bbff95362
#rb Zousar.Shaker
[CL 23848713 by Devin Doucette in ue5-main branch]
