I had a friend inquire about why a Studio template “Line Runner” he was using worked before publishing, but once it was published it would break. It turned out that for whatever reason the non-published place would set his character to R6, but when he published it allowed him to use what he had set as his preference on the site: R15.
If that game is played with an R15 character, it breaks primarily because CameraScript in StarterPlayer references “Torso” which doesn’t exist in R15 characters (should use HumanoidRootPart). Using Ctrl+Shift+F and searching for “Torso” brings up a number of results, so while the game is playable just by fixing the CameraScript, the place needs to be updated to support R15 in general. In fact, all of the Studio templates may need to be updated to support R15.