I encountered same issue. Image flashed with OOWOW will not boot. I tried Android 11 and 14 multiple versions, Ubuntu and CoreELEC. Installation completed successfully.
After flashing no OS booted properly, all ended in black screen with no error message. On CoreELEC there was error message once, that it failed to mount flash disk. Most of the time not even Khadas boot logo was shown. That error message failed to show on subsequent reboots, just black screen.
This was new Vim4 with OOWOW beta 250528.000 installed.
I also have older Vim4 with OOWOW beta 241112.000 installed, and that one works correctly.