I also specified a great value for the leeway setting (for the clock difference between the OO server and the Cloud server):
In my config.php:
'onlyoffice' =>
array (
'DocumentServerUrl' => 'https://oo.blah.com/',
'verify_peer_off' => true,
'jwt_secret' => '**********',
'jwt_header' => 'Authorization',
'jwt_leeway' => 2500,
),
Edit: updated successfully to NC 30.0.0 RC4