Hi & welcome! That's a lot of critters. When you repotted, did you remove the old soil? I think you would have noticed if those came from the new bag of soil.
What are we looking at in the pic? The pot where the plant lives? From when you repotted? Are you able to add a pic of the whole plant?
They look like millipedes to me, which eat decayed/decaying organic matter, which would include plant roots if they are not healthy, and stumps of dead leaves. If we are looking at the pot, that many millipedes are not going to find enough organic matter in soil to sustain themselves for long. Just like when worms are in a pot, the action of them eating the organic matter and then poo'ing in the soil will quickly turn the soil to thick sludge with no tiny air pockets, devoid of oxygen, which will suffocate the roots and cause them to rot and become palatable.
When you water, does brown water come out of the drain holes? That's a sign that some type of soil dwelling critter is poo'ing in there.
