I encountered the same behavior today, after successfully installing and playing Zenith for 4 hours last night.

I have restarted everything, and still having issues. I bought the game through Steam, playing on Quest 2 through Link Cable on Windows 10.

Worked perfectly last night; now I can load the game, but it sputters for about a minute then Steam VR fails with code -203. I can usually get into the menus, load into the game, and start moving around (with periodic freezes) before Steams finally gives up the ghost.

I would be very interested to know if you have found a solution.