Indexing fails with "Cannot decrypt this file..." yet file is shared with Admin account.

Nexcloud 27.1.8 // Ubuntu 20.04.4

Having installed Memories successfully, including dependencies for thumbnails etc, and configured it, we allowed it to index in the background.

In the UI admin panel, thousands of files are reported as being unable to be indexed.

Going to the command line and using: occ memories:index --retry we find that many files are skipped with the following error:

Failed to index file /nextadmin/files/[shared_directory]/[image_filename].JPG: Failed to get local file: Cannot decrypt this file, probably this is a shared file. Please ask the file owner to reshare the file with you.

Yes, these are indeed shared files. However the entire folder containing the file is correctly shared with the admin account and the admin is able to view, open, and interact with the folder and the images in the web UI.

Are we making a mistake, or is there an issue here?