Items that are in Shared update groups can't have their owner changed. The script handles this by removing the item from the group, then moving it, then adding it back to the group.

Some items, for example the parts of a story map, can't be moved one-by-one. They have to all be moved at the same time. If they are not in shared update groups, the API handles this seamlessly. If they are in shared update groups, though, the script is only removing one item at a time, so when the move is attempted it is not allowed.

I can think of at least two ways to fix this issue, but both would require major changes to the content moving code:

1. Recognizing that an item is part of a group and unsharing/moving/resharing all related items together at one time.
2. Move the shared update group management outside the content moving loop - that is, inventory all items in shared update groups and remove them up front, then run the content moving loop, then add all the items back to their corresponding shared update groups.

The ArcGIS API for Python user.items() method returns only 100 items by default. To be sure you're getting all items, these calls should be wrapped in a loop and run until no items are returned.

Right now the script itself requires an ArcGIS Online user account with admin privileges to run. I had add SSO login support but for some reason it stopped working and I didn't have time to debug it before my NEARC presentation.

A group can have a manager, which is different from a member or the owner. Right now the script only handles the latter two. Group Manager should be handled separately to make sure that it gets transferred over properly.

Thanks to @m3zito for pointing out this issue.