@Anna N I'm so sorry your micro greens failed! I didn't think it was possible to plant them too thickly. Maybe over watering? Is it possible that the warmth from your lights combined with too much moisture could cause mold to grow? I'm really guessing here...... I plant very thickly as you can see here. The somewhat more open area in the center was caused by a rampaging kitten. You can see the hardware cloth guard that I need to keep him out in the background. These are ready to use - they will go into a salad tonight.
This shows the container I use more clearly. Both are meant as plant saucers. I punched holes in the one containing the plants.
And finally, the problem child - the reason I need the guard. As soon as I removed the guard to take the pictures, he was there.