Thanks!
Thanks Mark. That should be fixed now.
I created a collection made of 5 routes. I later created 5 new routes & deleted the original 5, therefore effectively clearing the collection (ie leaving an empty collection).
I tried to use a Bulk Action to add the 5 new routes to the empty collection, but got an error message:
So I edited the empty collection and added 2 of the new routes manually, as normal, then went back to Bulk Actions & added the other 3.
That work as expected.
Mark