Points to ponder...

Miracle Grow has gotten quite a bum rap, and supports cannabis fine, if you take it's nutrients into considderation. The nutes will last a seedling around 4 to 5 weeeks or so. (depending on quantity and frequency of water poured-through, and temps) After 5 weeks in MG soil, I used to start 'em on half-strength doses of my veg fert and Superthrive. Full strength by 5 or 6 weeks or so.

What's in those peat pots? Is that what Miracle Gro Moisture Control looks like now-a-days? If so...you could use some added perlite, and remove the larger chunks of wood and bark. Gnats lay their eggs under that crap.

Would find-out about your ph asap.

Did you rinse the leaves after the insecticide spray(s)? (the insecticide can clog the pores in the leaves which restricts o2/co2 exchange...in other words...the leaves suffocate.)

Are you letting them dry between waterings?

No superthrive or other micronute, hormones or steroids? Spraying with anything other than fresh water and insecticides?

Fresh air provides fresh co2. Would open the closet up for as long as practical or possible.

As has been previously debated in other threads, I'm not a firm believer in the 24/0 light schedule. Especially if there is ongoing damage. Have you tried 18/6?