Heroic adventure - how do I unlock the next stage?

I just finished the first stage of the current Heroic Adventure. The next stage still just says “Complete all previous stages to unlock” but as far as I can see I have done so and it still shows the red lock. There is absolutely no indication that I can see of what else I need to do, the only thing I get if I tap on it is the parameters for the chest. What do I need to do?

Close the app, then restart it


Ah, your basic “have you tried turning it off and turning it back on again?”. Seems to be the answer quite frequently when something in this game messes up or looks weird.

It is, unfortunately