Sounds like you should disable thumbnails – https://docs.nextcloud.com/server/stable/admin_manual/configuration_files/previews_configuration.html?highlight=preview
Add the following line to your config/config.php:
'enable_previews' => false, Inside the
$CONFIG = array ( December 23, 2019 at 04:07PM
via reddit https://www.reddit.com/r/NextCloud/comments/eeheq4/problem_with_big_folder/fbvs1ro?utm_source=ifttt