If you log into MS Teams in regular (non-private browsing), Teams fails to load. This is apparently due to Intelligent Tracking Protection in Safari 11+, per https://docs.microsoft.com/en-us/microsoftteams/troubleshoot/known-issues/safari-intelligent-tracking-prevention-problems
Disabling ITP via Orion's per-site options pane works.
The "bug" is that logging into MS Teams in a private Orion window does not cause this to happen. Teams works with ITP expressly enabled in "private" mode, but not in "normal" mode.
This makes me wonder whether ITP is working properly in private browsing mode on Orion, since the above allows you to demonstrate that in "normal mode", ITP will prevent Teams from working, yet in private mode it will work without disabling ITP, therefore suggesting ITP is not functional.