seedlings stalled .... why?

I have successfully done 3 full grows on various strains of cannabis. The first grow was from grapefruit hybrid clones. They turned out very nice. Second and third grows were a cbd heavy strain called CB Dutch Treat. Both from seeds. First outing was very nice with good harvest. Second outing was subjected to some night time temps of just above freezing that absolutely stunted growth and dramatically reduced production. Grown using 24 hour veg and 12/12 flower. LED lighting.

Now to my problem. I started two seeds....one Black Sugar and one Cream and Cheese....both popped and grew tails in paper towel. I planted them in cups of ProMix HP Mycorrhizae. No nutes, no additives.
The seedlings came up quickly but then absolutely stalled. Stopped any development growth at all!
I ended up popping one more cream and cheese .... planted in a cup exactly like the first. I'm puzzled why 2 different strains would stall and another seed from the same batch is growing vitally. I have switched to a 250 watt MH in a 2x2 tent just to do some rough comparisons to my success with LED.

I guess my questions would be .... has anyone ever experienced a problem with seedlings where they just stop like that? And, what could possibly be the cause?

I'm hopeful that they might yet kick start up but I'm not holding my breath.

Soil looks soaking wet, any drainage?

Promix no nutes, start feed schedule

I’ve had promix hp grow seedlings way bigger then that. I vote overwatered. Promix hp claims to have a starter charge of nutrients.
If they were mine I would start fresh unless they were very special seeds.