Soma I've rewritten the code and it was the same but...another strange thing.
I thought it may be connected with pager so I removed rendering pager, disabled page numbers for this particular page and changed code to :
$pages->find('template=movie, limit=10')->not("youtube_id=''");
But it didn't show any results.
So I removed limit=10 and then it worked properly. Movies with empty fields didn't show up. But still I didn't have pager functionality, so I brought back rendering pager, enabled page numbers and added limit=10 again... and now it's working right... with the code and the same settings with which it was not working few minutes ago.
It's really strange and I have no idea what can be the reason of this behaviour

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