I kept having that happen to me on Temple of Anubis back when the OW Classic event was running. I got as low as 9 fps at one point. It was unplayable.
I truly dislike Clash with every fiber of my being. But I would still take it over Aatlis. Like, as much as I hate Clash I hate Aatlis more.
It’s really pretty, but just doesn’t play very well.