There is a new limit (500) to the number of items that you can have on your default wishlist. You can create a new category and make that your default and it will allow you to add again. Or you can clear out your default list and it will allow you again.

This is not a bug but a limit added so that people could move things from their unsorted list. You can still add things manually after 500. You just can't use the + wishlist function.

No worries! It is relatively new (a few weeks at most) so I can see you not being aware of it! Locking as resolved.