Unless there’s some insight by someone who happens to know more, for tracking this down, I think a kind of bisection would be best (yes, it’s a lot of work; some thinking and direct debugging is probably better done first). I think the first thing is whether Qt5 and the VTK/PCL update has this (to rule out Qt as the culprit). If that’s still slow, I’d go to the oldest VTK supported by the newest PCL (probably 8.90/9.0-ish for buildsystem reasons). If that is slow, push PCL back to the oldest that supports the new VTK build system. If that is slow, it’s something before and both PCL and VTK can be pushed back to the old build systems and bisecting within there. Otherwise, bisect within the new buildsystem.