When emulating a touchscreen device in Studio, it seems to be quite easy to break the emulator’s input mode if the UserInputService.MouseBehavior is in one of the Lock states.
After the first non-touch input in the emulator (e.g. alt-tabbing, moving the character with WASD, and sometimes even clicking in the explorer) touchscreen features like the dynamic thumbstick will be lost, and the real mouse will get locked so the emulated touchscreen can’t be used properly until MouseBehavior is Default again.