If you can't copy the log file to a flash drive with the tty, after starting with the standard boot option, can you try to get a picture of the screen showing the contents of the log file?
ps -A ? grep weston
beware that every 15 seconds the waylandloginmanager tries to restart the loginmanagerdisplay once its down, which causes the tty to change.
I'll add a maximum attempt in the next iso for the waylandloginmanager, so it displays an error, instead of showing nothing