It's not really a bug. That used to be the original path to the castle until it was replaced with a new path back in 2018, but since some older players still tried taking that path, I re-added the old one as secondary path, making both paths possible now.

Press Windows Key + R, this should open a small textbox.
Type in %appdata%..\..\LocalLow\LoE\Legends of Equestria - This should navigate you to your LoE folder.
In there should be a file called VideoSettings.json, you can open it and change the resolution there back to normal (1920x1080 for example) or you can delete the file to reset it to default.