Seed sowing 2022

I sow Sweet Peas in toilet roll tubes half filled with potting compost and topped off with seed compost. A sowing a few weeks back left a few tubes with "no shows" so the next sowing I just popped further seeds in these tubes and other fresh tubes. And yes, "no shows" again in these tubes though the rest of the sowing went well. All tubes used the same fresh compost when originally filled and the new tubes germinated fine. Time to tip them in the garden but I wonder why it happened twice.