Nextcloud selectively displays files to different users

I have just installed the Nextcloud server on a dedicated Raspberry Pi through a Docker container. I have a second container running the pi-hole ad blocker. I have also installed Nextcloud clients on a Mac (Mojave) and another Raspberry Pi running Raspbian stretch. For each of the clients I have been able to set up without any obvious error messages. The virtual drive shows up in each case.

Here’s the problem: if I create a file on machine A (user A), the file shows up in the Nextcloud drive and on the Nextcloud web site, but not on machine B (either its drive or its view or the server web site). The reverse is also true: if I create a file on machine B (user B) it shows up in the drive and on the server web site, but not on machine A (either its drive view or the server web site). Clearly the server sees both new files, but it only displays and syncs them with the user who created them, thus defeating the purpose of the syncing system.

What am I missing? Does the docker-compose file need special instructions?