Steps to reproduce:
Use vertical tabs and drag a tab onto another to create a tab group. The arrow (the one that hides/shows the grouped tabs), when clicked, does not always hide/show tabs. Clicking slightly to the left of the arrow works all the time.
Pressing the arrow itself hides/shows grouped tabs
Orion and macOS:
macOS Monterey, Orion version Version 0.99.108.1-beta (WebKit 613.1.10)