Bubbles or small scratches (also appearing like cracks) on the object are caused by small pieces of dirt or debris in the tank (vat) you are using. These small objects travel in the tank during printing, creating paths that resemble scratches as they move.
Make sure that the resin is 100% pure and free of small dirt particles. Filter the contaminated resin, for example, through a coffee filter. Also make sure your print tray is 100% clean and there are no dirt particles on the FEP film. Rinse the tank in warm water and then dry it with a paper towel.