See DevOps 3503, there's an error happening that isn't trapped during GetTarget and is actually being caught in the catch-all "_Error" handler. This is then calling TryCatch which is killing off the request (completing it) which is therefore causing the rest of the code to run but not work.
I want to see if I can simulate whatever's happening either by letting this page run indefinitely (Thread.Sleep for ages) or call Session.Abandon.