I am experiencing a strange bug in which no matter what, I cannot unlock level 4. Upon finishing Gale's level on any difficulty, I get the conclusion cutscene and then it does not save my score or unlock the next stage.

I had this bug once or twice with earlier characters, but a subsequent playthrough usually unlocked the next stage just fine - I have made sure not to skip through any of the cutscenes or score screen in case there is some checkbox not being marked, but I am entirely stuck.