Seattle Modified Jellies

Well my seedlings are struggling...not growing and two died....they seems fine first and then they dry up those two immature leafs and no growth comes from the middle, the roots are fine! i should take pics if those i have just started do the same....maybe heat mat bit it seemed alright first or not enough heat or lights they dislike or ph....lol maybe all of those and soil maybe i need to change....I am reusing it...something needs to change for sure!