Owncloud on Android really slow!

Quick recap:

Dual Core server with 4GB of ram. Ubuntu vhdx downloaded and installed.

Created a new user and installed on my android.

When opening a folder which has about 100 photo's it takes forever.

My phone is an Samsung S7. When my GF does this on her iPhone it works proper!

What is this?

Only error in the logs that I can find is:

Argument 8 passed to OC\Core\Controller\AvatarController::__construct() must implement interface OCP\Files\Folder, null given, called in /var/www/owncloud/core/Application.php on line 96 and defined at /var/www/owncloud/core/Controller/AvatarController.php#88

Its known that opening a folder for the first time takes longer /ages due to the preview generation of the pictures.