Rable Thanks for clarification.. .It sounds like you have set up the test account OK. If the account is displayed in iTunes Connect>Users and Roles>Sandbox Testers, and you can log in to iTunes on the device, then that bit all seems valid.
Yes, store listing was working fine in Jan. You probably know this already but the event process is something like this:
1. On start of layout, add the product IDs.
2. Then, also on start of layout, request store listing (you are prompted to login on the device I think if not logged already...)
3. It can take a few seconds for it to come back with a store listing result.
4. But once triggered listing success, write to a text box with 'Listing Success' so you know what's happening.
5. Also, use the condition "Is Store Available" to write 'YES' to a text box, so at least you know the store is available.
^^Sorry if that is too basic, but sometimes the small things matter!
I use an initialisation layout&event sheet that does the product IDs and store listing before going to the main home screen layout&event sheet.