I had this problem about two weeks ago. Not with Cyprus mulch but rather with pine shavings used as bedding for my uneaten feeder mice.

The water bottle for the mice leaked and soaked the pine. A few days later i had those little black bugs every where in my apartment. I traced there source to the wet pine and disposed of it.

I keep the unused pine elsewhere in a bag, and everything seems fine, no black bugs. This makes me think that they are moisture activated. So maybe replace your substrate and reduce the humidity in your snake enclosure?

Hope it works out!