Hakyll clean and build still has caching error

Question

I execute the following:

$ stack exec site clean
Removing _site...
Removing _cache...
Removing _cache/tmp...

And then:

$ stack exec site build
Initialising...
  Creating store...
  Creating provider...
  Running rules...
Checking for out-of-date items
Compiling
  updated css/default.css
  updated images/haskell-logo.png
  [ERROR] Hakyll.Core.Compiler.cached: You are trying to (perhaps indirectly) use `cached` on a non-existing resource: there is no file backing index.html

How can I truly clean my hakyll site such that it builds?

(More code here: What's the root of a Hakyll site? )