Ok I got it going - but had to comment out in SystemHealth.php:
// foreach (new \RecursiveIteratorIterator($directoryIterator) as $file) {
// if (strpos($file->getPathname(), '.git') !== false) {
// continue;
// }
// nlog($file->getPathname());
// if ($file->isFile() && ! $file->isWritable()) {
// return "{$file->getFileName()} is not writable";
// }
// }
Not sure why - but that was what was stopping it.