I don't use those cubes or any propagator for seeds. Rockwool is too damn finicky to get seeds started and going ime. Clones run just fine in em, but seeds... I've lost way too many to damping off or simply rotting to consider RW a viable germination media at this point. That being said, those cubes look way too wet.
What EC solution are you spraying at them? What pH?
Even with clones, when I get them loaded into their starting cubes, I start the cube saturated and let it be for at least a weak in 99% humidity. That RH isn't ideal for seedlings, but the cubes should stay moist enough to sustain life for at least a few days at normal propagation RH. I even started some lettuce in RW cubes just as a proof of concept for a side project I'm working on and they germinated just fine using the same exact method I use for cloning.
The lesson being so long the cubes never dry back to bone dry, and you get approximately 30% dryback (30% less wet than when you last watered) then you should be in alright shape to avoid damping off.