Steps to reproduce:
When moving a tab to another group from the context menu, the tab reappears as a weird "ghost tab" that cannot be selected. Also the tab next to it disappears (although the tab preview still shows it). Quitting & reloading Orion fixes this. The moved tab also won't appear in the other group before the reload. See the video.
Orion, OS version; hardware type:
Version 0.99.124.3-beta (WebKit 6188.8.131.52.1)
MacBook Pro (macOS Big Sur 11.7.7 build 20G1345)
In the video, see how the Apple tab reappears after I click on the leopard tab. And see how the leopard tab disappears when I click on the tab with the red "A". When you see the pointer hovering over the Apple tab, I am clicking it.