I ran it through a few times and it worked fine, I couldn't get it to to freeze or not progress. When it stops working for you can you see in the debugger that the variable has been set correctly? It could be that somehow the game is losing focus and not registering the mouse input. It could be worth adding a keyboard trigger to progress the dialogue also.
Thank you for testing! I could only recreate it in project preview so it is possible it is losing focus as you said. In debug mode it works perfectly so I have no way of seeing what the issue is. I'll implement a keyboard method so when the player keyboard mashes it will hopefully continue.