For those having issues with crashes, from the Discord:

LordPandamonium - Yesterday at 9:18 PM
Issues with stamina and the world defensive stages are usually the result of not clearing cache when the new stages are added. If you are still experiencing issues, please leave your nutaku ID

So if after clearing your cache you're still experiencing these problems head over there and leave your ID for them.

Unregistered: Doing the missions now for no reward seems worse than doing them later for only a small drop chance. Small chance is better than none.