That description sounds similar to some bugs on a phal of mine that recently succumbed to crown rot. They seem to be feeding off of the rotted part of the plant as I haven't seen them in media or on the roots. They were tan and moved very quickly. I poured some more hydrogen peroxide on the crown where they were and haven't seen them for a few days so I'm waiting to see if they pop up again.
However I don't know if they are the same thing as yours though if your plant is healthy.
And yes I do still have said phal as all of the roots are still fat and green a week later. I'm holding out hope that the meristem tissue was not damaged, but I'm not counting on it.