Just to start, I have submitted a ticket in-game but I wanted to see if anyone from the community has any input as the ticket system seems to take well over a day to be processed.
The Proving Grounds seems completely inaccessible right now. I have tried looking at class trainers for every character I have, checking Garrisons on every character I have (which used to be the way I accessed it pre-shadowlands), and even doing the Kun’lai questlines through the White Tiger Temple trying to access it straight from the source. As of right now I cannot access it.
Proving Grounds had a series of achievements and titles associated with it that add play time to someones account, i.e. it’s free content that was already implimented into the game and I don’t really see a reason why it was removed, if that is the case.
Some Hidden Artifact Skins, such as Unholy Deathknights, are most effeciently farmed out through the Proving Grounds as you can basically spend a couple hours soft resetting for Apocalypse and Army of the Dead in order to try and get the book to spawn. Without access to the Proving Grounds, this had made farming out RNG spawn drops such as this a lot harder and more time consuming to get.
The Proving Grounds, albeit most of the community disliked it, but to some were a fun way to test how well you know your class. It allowed you to really push your character in a solo environment that you could do on your own time, utilizing CDs and CCs in order to see how far you could really go. With the Bronze requirement being removed for Heroic Dungeons, I understand that it’s “forgotten content” but it still has it’s uses. If this was mistakenly removed or bugged out due to the Shadowlands squish then I understand, but it should be made accessible again.
Edit: Please see my comment down below for instructions on how to access. This is as of Shadowlands Patch 9.1.5