I'd never seen this kind of pest before. Recently I tried to start seeds and cuttings, the seeds I planted was already germinating before I put them in the ground, but then they never showed up. That's when I decided to dig them up and found that the sprouts became mush with tons of tiny thready worms inside. The cuttings on the other hand are getting symptoms of fungus gnats, so I dug them out and encountered with the same problem. There were an obvious damage to the ends of the cuttings that was caused by the worms. At first I thought they were fungus gnat larvae, but on closer look it's nothing like I've ever seen.
I'll post a link to a video of it, sorry about the quality of the video.
I'll post a link to a video of it, sorry about the quality of the video.