I bought a lavender from home depot, and it was growing good, but after an animal dug really big holes around it (I put some compost in it), it started dying. It is now dead, and I would like to find the cause of death. It also has mulch, Kellog potting soil, scotts premium topsoil, and expandable coconut seed starter.
I think you have answered your own question already, it started dying after an animal dug holes around it. So I think the rabbit might have damaged some of the roots. Why that rabbit was digging there is another interesting question. You seem to have put your plant in a very interesting substrate (from 4 different sources, if I count well). It might be that that attracted the rabbit. I don't completely understand why you mixed all these substrates together, to be honest. I have lavender growing here in clay soil (Netherlands is clay, clay and more clay), it grows fine. If you really don't trust your clay soil for it, I think just filling a hole with potting soil would be enough.
If you want to replace this dead plant, you might want to consider taking cuttings somewhere. Lavender can easily be propagated via cuttings. It's fun and for free!