In ServiceIndexResourceV3Provider.TryCreate(), when there are errors connecting to a v3 feed, the method returns (false, null). This allows fall thru and cause the feed to be treated as V2. We should stop the fall thru instead.
Fix of NuGet/Home#1253: Don't fall thru when v3 feed failed
Now if there is a failure, an exception will get thrown so GetResource fails immediately so no fall thru will happens. Also the V3 resource is cached only when it is successfully created.
Fixed with NuGetArchive/NuGet3@11a75e0