Thanks - that worked. If anyone from Apple is listening, I would like to suggest that this is a very awkward workflow for someone who likes to add, subtract, & tweak the order of photos to achieve just the right effect. It should be possible to create a shared album that preserves the sort order of the pictures that were added to it in a group, or at the very least, rearrange photos in a shared album.
Shared albums are still the shared streams the used to be in the beginning. A potentially long stream of photos where we can drop occasionally a few photos to share them with friends. And when the photos arrive in the friends or families shared albums the new photos will appear at the end of the stream, so we quickly can identify new photos. When Photos has been released, the Shared Streams have been renamed to "Shared Albums", but the behaviour did not change. The term "Album" is misleading. They are still streams, even if the name "Album" suggest they can be used like albums, and arranged and sorted as we want them to be sorted. It is a communication channel to exchange photos between several persons, not a web gallery of albums, like in the good old Mobile Me days.