Very slow quicklook

Lost one day to find that Totalfinder was the responsable of very slow quicklook !!

Mac Pro - Mojave 10.14.6

This is highly unlikely. TotalFinder does not interfere with QuickLook. My bet would be that you killed process (with TotalFinder running inside) and just the fact that you launched fresh fixed the issue.

Or is it reproducible? (Fresh with fresh TotalFinder injected into it)