Are you sure that the reducer and hardner are compatible with each other. In the past if in doubt I always spray and paint some type of test panel. I have found that not all hardners work well with all paaints. I have found that if they work against each other a grainy type effect will result.
I have always made it a practice to by all the paint, reducers, and hardners from the same source. The same name brand elimates risk of a less diserable finish and problems.
Also I have run into a problem when not using the right primer which tends to react to the paint.
