SUMMARY
I'm trying to use it to obscure a license plate in a video, using kdenlive-19.08.1-x86_64.appimage on ubuntu.  The red rectangle that's supposed to surround the obscured area often doesn't - it's around some other random spot on the video.  Several times parts of the video I've already done have become unaligned, and I've had to do them over again.  I just tried to add a second auto mask to a section of the video, and dragging that one around caused the other one to move to a randomly different position.  It has crashed on me a couple times.  I'll go to the beginning of a clip, click auto mask's analyze, it won't get the alignment quite right, I'll do exactly the same thing again, and it'll get it right.  I don't know for certain that that part's a bug, but if that randomness is intentional it would surprise me.  

The motion tracking is pretty disappointing.  I wonder if that could be related to the misalignment of the red box with the obscured area - maybe it's doing tracking based on the position of the red box?

(Not really related, but I'd much rather have a single solid color than pixelation, since with enough frames, pixelation can be reversed.)

STEPS TO REPRODUCE
1. Try to use auto mask

OBSERVED RESULT
Sadness.

It's tough to tell what of the console output might be useful from my last crash, but here's the end of it:

################### ClipController::updateProducer
################### ClipController::addmasterproducer
################### JOB finished 426
################### loadjob COMMIT
################### ProjectClip::setproducer
################### ClipController::updateProducer
################### ClipController::addmasterproducer
################### JOB finished 323
################### JOB finished 415
################### JOB finished 407
################### JOB finished 411
/tmp/.mount_kdenliUzw0iw/AppRun: line 26: 13726 Segmentation fault      (core dumped) kdenlive --config kdenlive-appimagerc $@