Apple ID prefix change in TestFlight build all of a sudden - Should I be concerned?

Question

I noticed that all of a sudden in our latest TestFlight build, users now have a different Apple ID that Apple provides to our game application compared to when they are playing our app not on TestFlight (publicly available and launched free to play game). Specifically, our original Apple IDs had a "G" or "U" as a prefix (we use Game Center to log them in), but now those same users who switch to TestFlight register with our backend as new users with a "T" as the prefix (to be clear, the entire ID is changed but the prefix is most notably different). If the user switches back to the non-TestFlight public version of the game on the app store, their ID goes back to using the G or U prefixed ID.

Is this new functionality? It wasn't like this for the past year we've been developing for iOS. Should I be concerned?

Additional Context: We had to switch our app from using only consumable IAPs (can be purchased multiple times) to also using durable IAPs (can only be purchased once). There was a modal from Apple about us changing business models and we had to answer a bunch of questions and right around this time we switches is when we started noticing this new ID behaviour. Coincidence?

I basically am looking for reassurance that when we deploy our new build, all of our users won't suddenly have all of their IDs changed because our new build is "different" than before and are now on some different kind of ID system. I'm pretty sure that is not the case but I want to make sure that this is just some kind of new TestFlight functionality and that when we deploy our new build, all of our users won't suddenly lose their accounts because their ID's all have changed.