When adding new elements to a Map in blueprints it will return the error "Cannot add a new key to the map while a key with the default value exists". This is because it currently won't increment the default value when adding a new key.
The easy workaround is to just edit the default key and then it will be able to add another element. It would be more intuitive if it automatically incremented the default key value though.
You get an error message "Cannot add a new key to the map while a key with the default value exists"
A new element gets added that has a key that is incremented from the default value. e.g. If the default INT is 0 when you add another element the next key is automatically set to 1 then 2 etc...
Head over to the existingAnswerHub thread and let us know what's up.