Try removing 3rd party qlgenerator files & see if that helps.
/Library/QuickLook
or ~/Library/QuickLook
is most likely.
Drag them all out & reboot.
(/System/Library/QuickLook
ought to be Apple qlgenerators, so I'd leave that alone for now.)
If you're fixed, eliminate by halves - drop half of them back in, reboot again - if it's still OK, then the suspect is in the other half.
Keep halving til you find the one.