Strange sim speed change on save/reopen

[KenTanker0us]

Hello friends, I'm experiencing a strange slowness when I sim after re-opening a scene. I've been able to re-create it a number of times.

I create an FFX grid, add an Object Source helper, make a small sphere, add it to the helper, add that helper to FFX. Move the sphere into the lower center of the grid.
Turn off fuel, smoke only. Set my directories.

This sims SUPER quick. A little sphere emitting smoke.

BUT...

Now I save it and re-open it. The sim is DOG SLOW. I wonder if anyone can offer any insight? What am I doing wrong?

I appreciate any and all advice.

Ken