I think that is a really bug beacause :* filerun create a shadow folder who contains thumbnails in your folder where are your pictures* creation thumbnails is very slow.
* and it's impossible to create thumbnails for ARW format pictures. Usely, ImageMagick know this format.
FileRun Version : FileRun_2019_05_21_PHP_71-73NexCloud version : Nextcloud-2.5.2
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