I had a similar dist which was failing for users and I could not figure out why (through like 4 releases of just looking stupid twiddling stuff and waiting to see if the tests passed; mine always did). It was related to prereqs not being installed even though I was declaring them. I finally added explicit versions to everything as well as some modules that the prereqs called but my code didn't and that fixed it for testers.

Your tests seem to be crashing at the junction of Exporter + 5.6 + Darwin (and maybe Params::Validate is related though its tester report doesn't seem to agree). You could make a note of that in the Pod/Changes/README until you get it sorted.