After a Maintenance Mode reset the TV Box needs to authorise your Boost subscriptions and purchased content rights. TTG216 just means the box hasn't acquired the necessary authorisation. And I know you've gone through this at least once before so I know it's getting a bit wearing.
Make sure the TV Box is connected to the router and has an Internet connection. If it doesn't it'll tell you.
Then on the TV Box remote
So, that should have got the software and players updated if needed or at least ticked a check box. And the subscriptions should have been authorised.
I can only suggest you let the OCE / TV Team look at your account setup and the TV Box logs. The TTG-216 error says the content isn't available but if your account is showing the content is available to play in the Rented & Owned tab on the TV Box then taking you back to a purchase screen isn't expected.
When you say your account is showing 4 copies of the movie - that's on the TV Box in the Rented & Owned tab in More TV > My Stuff ? Is that right? And presumably one or more are expired rentals? But when you select one to play it asks you to purchase again?
Or when you say your account is showing 4 copies of the movie is that just in the purchase history? Excuse my asking but I'm just trying to get my head around how this situation can arise. And just so you're aware, I'm a customer so don't have access to any of your account stuff to see what you're seeing.