I did not yet catch the exact pattern when this happens, but from time to time (pretty often recently) when I open Orion I see no tabs (no Start Page tab, too), with a URL already filled in (probably from my previous session) and no reaction to changing the URL.
Browser restart resolves the issue.
I would expect a new Orion window to always have at least one empty tab ready for navigation.
0.99.127-rc
Sonoma (14)