Hi Sarah
Your compost is not necessarily the problem. I found the same happens with some bought in compost, especially those with a finer texture such as those containing peat, and when the compost gets too damp, which is likely at this time of year.
It can also happen when the soil surface is pressed down. My dad taught me to avoid this when potting up and filling seed trays by pressing the compost into the pot until it is nearly full and then sprinkle a layer on the top and not press it down. Watering seed trays and pots from below helps. For compost in beds I would just hoe if the soil is damp or has the green algae on it. This will loosen the surface and and help dry it off. Good ventilation will also help.
Barbara