I have the same problem in Unity 2019.3.0f6. Every time I play the project, a new atlas is created for my sprites. And I noticed that this problem also generated a size of 3.6 GB of the "AtlasCache" folder. I was able to reduce this size to 6Mb by deleting the "Library" folder and re-porting the project. But that did not stop Unity from generating new Atlas each time it was played in the Editor. I use Anima2D in my project, I don't know if it can be related.