I bet the brand is not one of these: Sherwin, Ben Moore, or Kelly Moore.
I bet you obtained the paint from a Home Center.
There is only product that you cannot shake and that is any polyurethane stain. Poly has to be stirred because of just this thing.
I would first inquire at the place you bought this for them to check it out. Bubbles are not normal in any paint application. You might get new paint and an allowance. What did the directions on the paint can read?
Lightly sand again and use one of the real paint products.