A potential issue with /execute, when executing it with animation_controllers, can cause the game to crash under certain circumstances, here's how the bug triggers

 First, we need to prepare a behavior pack that adds an animation controller to the player.  This controller executes "/execute run testfor @s" (or similar)

 Next, prepare to create a new world, this world needs to open "Upcoming Creator Features", and then enable the prepared behavior pack

 Create a world, then go to the end, then return to the overworld through the end portal (you can kill the dragon to generate it, or you can build it manually)

 The End Poem will appear when returning to the Overworld through the portal for the first time from the End, however, with this behavior pack installed, the game will crash when the player reads the End Poem through the portal

 This bug was first discovered on BDS, and after local testing, a specific trigger method was found.

English is not my native language, the above text is translated by Google, please forgive me if there are any mistakes