Why did cps call and ask to come to my home?

I went to court because my ex wife had a cps case opened on her where i got physical custody of our child. She had failed then past a drug test. I was told the only reason i had to go was because it involved my child. She was given classes and i was given nothing. Im not sure if she put out any allegations on me or not. I provided my own clean drug test from my doc but it was never asked for. my ex has a criminal record but i do not while being over 18. they called and asked some questions then gave me a date and time they would be coming to my home. Why is this?