
It only ever appears when I try to open an individual level; opening an episode through the launcher or using the "Start Game" option in the LunaTester both work, but opening an individual level in such a way that the testing GUI is present doesn't. Furthermore, opening a .wld file also works.
I even tried doing a fresh reinstall of the game, but nothing changed.
If you need any more information to help figure out what's going on, ask away. I'm desperate to find out what's causing this and take whatever measures necessary to fix it.