Just installed CI4 RC1 but getting blank pages

I have the exact same issue. Fresh install, windows/xampp, i have other sites working on CI 3. This was a fresh install with composer (done yesterday), error log just shows home controller loaded, blank page.

if i remove:

while (\ob_get_level() > 0)
{
\ob_end_flush();
}

\ob_start(function ($buffer) {
return $buffer;
});

from events.php it works, with code back in blank page.