I think this is actually kinda-by-design, but I just spent a half an hour pulling my hairs out, so even if this is not a programming bug, this is definitely a UI/UX bug. To reproduce: 1. Start with a blank slide 2. Add any element and select it (I used an image) 3. Go to animations for that image, click "+" to add a new animation. This now appears in the animation list. 4. Select animation Category "Motion Paths" 5. Click on the Effect "Free-form Line" At this point the Animation list becomes empty again. It seems that selecting "Free-form Line" deletes the newly-created animation from the list. Only if you now move your mouse back to the canvas you can notice, that the cursor has changed and is now expecting you to draw your line. After you draw the freeform line, the animation entry re-appears in the list. Also - and this IS a programming bug - it is obviously a new entry, because if I had changed other attributes of the animation (like Start condition or Delay), those are reset. If a video is needed, I can supply that too.
I can reproduce the steps in LibreOffice 7.2.5.2, under Kubuntu 18.04, x64. In my opinion, even if the process of defining the animation hasn't ended, it shouldn'd disappear from the list.