No previews in search/smart folders

[Immateria]

I am unsure whether or not this is by design, but while the files I am referring to(a bunch of .mkv) have previews if I navigate to their directory, they do not have previews in a search or in my smart folders.

Mac mini 2012 i5/4GB on 10.13 High Sierra

[Marginal]

I sometimes see this. Looks like a Finder issue since this plugin isn't called to render the missing icon.

[Kagami]

I have a slightly different issue: thumbnails in Finder search are (mostly) fine but I don't have thumbnails in the quick Spotlight search (the one which you open with Cmd+Space/F4). But metadata (duration) is displayed correctly and I can even see the full thumbnail if I press Space. See screenshot.

What I've tried:

• mdimport -r "/Applications/QuickLook Video.app/Contents/Library/Spotlight/Video.mdimporter"
• mdimport -i /path/to/folder
• killall -9 com.apple.quicklook.ThumbnailsAgent
• killall Finder
• Re-enabling Quick Look extension
• Re-index all Spotlight database
• Reboot

Some commands help to unstuck thumbnailer and it fixes missing thumbnails in Finder, but not in quick Spotlight search. Any ideas?

[Marginal]

Will be fixed in the next release.