To me that looks like you've sprayed a little too far away, which has enabled the lacquer droplets to partially dry before hitting the surface. Spraying is a dark art, the unholy trinity of temperature, thinner and distance. A change in one requires some testing to get the other two right. Humidity, ventilation and air pressure add complexity to the formula...
If it's cold, the lacquer is stiff so you need to add thinner for an even flow and a short enough drying time to prevent runs, and then find the right distance to keep the lacquer liquid until it hits the surface
If it's hot, the lacquer is more liquid and will dry faster so less thinner is needed. Again you'll have to find the optimal distance.
If the shooting pressure is low, the droplets run slower allowing them to dry during the travel. Again, test.
Regarding sanding, I've always sanded lacquer wet since it both seems to be smoother and keep the dust out of my lungs. Use a block on flat surfaces and be extra careful not to sand through the edges. Use no pressure at all, the weight of the block is plenty enough, also flush the paper and wipe the slurry often. My choice to start with might be 600 grit, 400 might be too aggressive and 800 too slow which could make you use too much force, causing the abrasive slurry lumps make deep scratches. Your aim is just to knock the tops off of those micro lumps. If you manage to level the surface to a satin matte you're golden.