File and directory permission change -> log errors

I use OpenMediaVault 3.0.72

PHP: 5.5.30
MySQL: 5.5.55
Nginx
fail2ban
letsencrypt
Nextcloud 11.0.3

I installed Nextcloud through webinstaller and everything worked out fine (According to this installation guide).
To harden my cloud I applied the permissions from this HowTo. Afterwards I get WebDAV erros like:

Sabre\DAV\Exception\NotAuthenticated: HTTP/1.1 401 No 'Authorization: Basic' header   found. Either the client didn't send one, or the server is misconfigured, No public access to this resource., No 'Authorization: Basic' header found. Either the client didn't send one, or the server is misconfigured

[internal function] Sabre\DAV\Auth\Plugin->beforeMethod(Object(Sabre\HTTP\Request), Object(Sabre\HTTP\Response))
/srv/dev-disk-by-label-Storage/nextcloud/3rdparty/sabre/event/lib/EventEmitterTrait.php - line 105: call_user_func_array(Array, Array)
/srv/dev-disk-by-label-Storage/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php - line 466: Sabre\Event\EventEmitter->emit('beforeMethod', Array)
/srv/dev-disk-by-label-Storage/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php - line 254: Sabre\DAV\Server->invokeMethod(Object(Sabre\HTTP\Request), Object(Sabre\HTTP\Response))
/srv/dev-disk-by-label-Storage/nextcloud/apps/dav/lib/Server.php - line 231: Sabre\DAV\Server->exec()
/srv/dev-disk-by-label-Storage/nextcloud/apps/dav/appinfo/v2/remote.php - line 30: OCA\DAV\Server->exec()
/srv/dev-disk-by-label-Storage/nextcloud/remote.php - line 165: require_once('/srv/dev-disk-b...')
{main}

and

Sabre\DAV\Exception\NotFound: HTTP/1.1 404 File with name Uploads/2017/04/DSC_0995.JPG could not be located

/srv/dev-disk-by-label-Storage/nextcloud/3rdparty/sabre/dav/lib/DAV/CorePlugin.php - line 81: OCA\DAV\Connector\Sabre\ObjectTree->getNodeForPath('Uploads/2017/04...')
[internal function] Sabre\DAV\CorePlugin->httpGet(Object(Sabre\HTTP\Request), Object(Sabre\HTTP\Response))
/srv/dev-disk-by-label-Storage/nextcloud/3rdparty/sabre/event/lib/EventEmitterTrait.php - line 105: call_user_func_array(Array, Array)
/srv/dev-disk-by-label-Storage/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php - line 479: Sabre\Event\EventEmitter->emit('method GET', Array)
/srv/dev-disk-by-label-Storage/nextcloud/3rdparty/sabre/dav/lib/DAV/CorePlugin.php - line 253: Sabre\DAV\Server->invokeMethod(Object(Sabre\HTTP\Request), Object(Sabre\HTTP\Response), false)
[internal function] Sabre\DAV\CorePlugin->httpHead(Object(Sabre\HTTP\Request), Object(Sabre\HTTP\Response))
/srv/dev-disk-by-label-Storage/nextcloud/3rdparty/sabre/event/lib/EventEmitterTrait.php - line 105: call_user_func_array(Array, Array)
/srv/dev-disk-by-label-Storage/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php - line 479: Sabre\Event\EventEmitter->emit('method HEAD', Array)
/srv/dev-disk-by-label-Storage/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php - line 254: Sabre\DAV\Server->invokeMethod(Object(Sabre\HTTP\Request), Object(Sabre\HTTP\Response))
/srv/dev-disk-by-label-Storage/nextcloud/apps/dav/appinfo/v1/webdav.php - line 60: Sabre\DAV\Server->exec()
/srv/dev-disk-by-label-Storage/nextcloud/remote.php - line 165: require_once('/srv/dev-disk-b...')
{main}

for core

Accessing the API class is deprecated! Use the appropriate services instead!

OC\Tags::getFavorites, exception: Could not find category "_$!<Favorite>!$_"

I can’t remember the initial permissions to restore them. How can I avoid this debug-message?

You need PHP 5.6 or newer:
https://docs.nextcloud.com/server/11/admin_manual/installation/system_requirements.html

I actually use PHP 5.6.30