Why is my very old Entry Point redirecting to the Home?

I finally got to Ent v12 in my production instance (now working on v13/v14) and unfortunately didn't notice in our testing that an Entry point that was added in v6 stopped working and now redirects to the Home page, oddly I've accessed it a couple of times just fine, but now seems to always redirect.

Yes, it's old, and yes "Entry Point" Face palm , but it's a monitoring page for an integration with an older system that we are moving away from, so I need it to work for another 6 months or so and honestly don't have the time or the will to do more throw-away work.

Any thoughts on why it's redirecting and how to stop it doing so?

Thanks,
FrancescaS