Use a heavy nap on the roller.. Make sure paint is mixed properly ie add a bit of water.. And put 3/4 coats on.. It might work.. Or get it re skimmed..

Hi Peter. Sometime's when painting an uneven surface the paint may seem to look patchy, this is normally due to the way the light bounces off the wall. If the the wall is very uneven then the chances are the patches would of been visible prior to painting ? and they will probably be rough because when sanding an uneven surface,if not careful bits will get missed. To fix this i would recommend filling the patches or skimming the wall. But i don't recommend applying too many coats of paint now if the wall is not flat. If you have a couple of solid coats of paint on the wall and it's still patchy, don't waste any more paint.

It sounds to me like it may just need additional coats. Contract matt is thin and may take more layers to get good opacity, also when rolling out the walls try and make sure that the roller doesn't run dry as this will take the paint off the walls rather than put it on. Try a trade matt like Dulux it is much thicker and will take fewer coats. Keep the brush loaded with paint don't let it run dry. Start at one end of the wall and roll up and down starting at the middle point between the ceiling and floor. Top to bottom one strip at a time. Reload your roller and roll another strip top to bottom blending it in with the previous one. Other reasons for patches are wet or porous surfaces. Make sure the walls are clean and dry, and any porous surface like where spots have been filled or bare plaster needs sealing or mist coating.