2001 Ford Taurus Bubbles in tranny fluid

I noticed air bubbles in the tranny fluid, few weeks ago(when it was shifting bad), the fluid level was not too full / not too low.

I spoke to a shop, and on his advice, I added 1 quart of ATF, and the bubbles disappeared for 2 weeks, and then they re-appeared after 2 weeks.

This time, I added another 2 quarts of ATF, and the bubbles again dis-appeared for 2 weeks, and re-appeared again. The tranny now has lot of fluid.

There is no leak in tranny, I got it checked by the shop.

Yesterday night after driving 40 miles, I checked the fluid, and there were no bubbles.
Today morning I checked again after same 40 mils drive, and the fluid was full of bubbles.

I dont know what changed in these 2 trips, which is causing bubbling.
The fluid is in good shape, and there is no leak in the Tranny.

Kindly advice !

If the car is driven by removing the Tranny dip-stik, can it cause air bubble in fluid?