Shared link not working?

I am on NC: 18.04
I share a directory via “shared link”. (containing pictures/jpgs)
External user can open/see this directory and the previews, but when clicking on one picture you only get the “circle”/waiting and no picture.

And nothing in the debug logs with:
“… ‘debug’ => ‘true’,
“log_type” => “file”,
“logfile” => “/tmp/nextcloud.log”,
‘logfilemode’ => 0640,
“loglevel” => “3”,
“logdateformat” => “F d, Y H:i:s”,

could someone please point in the right direction?