Sounds similar to the soil mites (they had some type of mite, soil were our best guess as they only wanted to hang out in the roots) we had when we bought a few neo falcatas. Putting them in S/H and blasting them with neem oil seemed to cure them. Though, we have had a real issue with getting rid of them 100%. Could also be predatory mite. Simply my guess. You can google image and compare.