My guess fungus gnat larve. do you have small flys buzzing around. In any case I would try mosquito bites. Crush them up and mix in top two inches of soil. This contains a pathogenic bacteria that kills larval stage of soil bearing insects. Harmless to humans. Be patient takes a while to disperse into soil through watering. Hope that helps.
you must catch one and id it asap.
I just caught a few root aphids after I id them I found they came in with some store bought idaho potatoes.
Sure enough the bag started hatching within 3 days.
Root aphids can wipe out a cannabis crop be careful.