Yeah, even with 280 PPFD, 10 cm distance is way too close for seedlings – the proximity itself causes stress from heat and intensity, regardless of measured PPFD. The yellow spots and stunted growth are classic early light stress signs. Raise the light to at least 35–45 cm and keep RH in check – 70–80% is a bit high unless you're running perfect airflow. Give them a few days and they’ll bounce back.