We know how it spreads. It's not from mulch. Not saying it couldn't happen, but I doubt the mites would survive being chopped up and then composted.

I doubt it too with commercial mulch and their composted temperatures. I am concerned that another vector for this disease might be aphids as they mimic the mites in terms of their sucking parts of the sap.
Currently from what I understand, there is not enough research money or someone setting up a scientific study to determine if aphids are another vector of this disease.

I bought a bunch of bags of mulch this weekend. I forgot to put out two of them. So last night I opened them and put them down. The mulch was so HOT!. I hope that killed all the weeds I put it over.

Those bags sit out in the sun at Home Depot or whatever. I'm not sure the mites could survive that. But still, don't put a RRD bush in the landfill or compost!