Failure of azure data factory integration runtime with Vnet enabled

I had been using Data Factory's integration runtime with VNet successfully, but it recently stopped connecting to Cosmos DB with the MongoDB API (which is also within a VNet). After setting up a new integration runtime with VNet enabled and selecting the region as 'Auto Resolve,' the pipeline ran successfully with this new runtime.

Could you help me understand why the previous integration runtime—configured with VNet enabled and the region set to match that of Azure Data Factory—worked for over a month but then suddenly failed? The new integration runtime with VNet and 'Auto Resolve' region worked, but I'm uncertain if the 'Auto Resolve' region contributed to the success or if something else allowed it to connect. Error:Failure happened on 'Source' side. ErrorCode=MongoDbConnectionTimeout,'Type=Microsoft.DataTransfer.Common.Shared.HybridDeliveryException,Message=>Connection to MongoDB server is timeout.,Source=Microsoft.DataTransfer.Runtime.MongoDbAtlasConnector,''Type=System.TimeoutException,Message=A timeout occured after 30000ms selecting a server using CompositeServerSelector{ Selectors = MongoDB.Driver.MongoClient+AreSessionsSupportedServerSelector, LatencyLimitingServerSelector{ AllowedLatencyRange = 00:00:00.0150000 } }. Client view of cluster state is { ClusterId : "1", ConnectionMode : "ReplicaSet", Type : "ReplicaSet", State : "Disconnected", Servers : [{ ServerId: "{ ClusterId : 1, EndPoint : "Unspecified/cosmontiv01u.mongo.cosmos.azure.com:10255" }", EndPoint: