Level Streaming Volumes: TravelFailure: InvalidURL, Reason for Failure: 'Invalid URL: /Engine/Maps/Entry'. Shutting down PIE.

I’m creating a multiple level VR walkthrough and I keep getting stumped at the same hurdle. The 8 levels are linked up with streaming volumes and a level sequence moves the player through the scenes, unloading the level as they enter the next volumes. It has worked all the way through a number of times (only when I create a brand new project file), otherwise it will cause the below error halfway through the sequence. If I begin the sequence from just before the halfway point, it occasionally works, and carries on through to the next level…

What I don’t understand is that the Level names and their references in the blueprints are correct, and there doesn’t seem to be any issues with the Streaming Volumes.

Warning TravelFailure: InvalidURL, Reason for Failure: ‘Invalid URL: /Engine/Maps/Entry’. Shutting down PIE.
Warning TravelFailure: ClientTravelFailure, Reason for Failure: ‘Invalid URL: /Engine/Maps/Entry’. Shutting down PIE.

I can’t get my head around it at all. Anyone had the same issues or now what can cause this error?

Thank you!