Last Week, Update 4.5 was released to Fortnite, one of the new features should be the Playground, but as soon as the patch was online it came to first problems with the new feature.
So the Playground LTM was again deactivated, officially no details were mentioned, one mentioned only that the Playground LTM on 29 June will be available again.
Meanwhile, but another post was published, there are still problems that you could not solve yet. The title says that the playground will be reactivated on the 1st of July, but in the article the next information will be published on Monday the 2nd of July.
So it seems like you need a little more patience until the playground is available again, maybe you can accelerate and train again on Sunday or Monday!
Source: Epic Games