I'd bet money its Arch. I love `pacman` but the package spam for Haskell is a bit much as its automatically updating everytime a new package is hosted on hackage. I'd recommend skipping it all together, just use stack and build it from source, let stack manage GHC and you'll never update except when you want to.
To add some context to this, the reason why packages which depend on haskell in arch are such a mess is because "the arch way" is to dynamically link everything. This has its advantages (namely security), but is not super compatible with the haskell ecosystem which is designed with static linking in mind.
Like my parent commenter, I recommend just doing everything through stack. stack-static from the AUR [0] is the convenient way to do this (rather than dragging in a few gigs of ghc dependencies for stack only to have stack create its own local ghc installation as well).
If I'm not mistaken, Arch has some ornery maintainers in the Haskell department as well. Pandoc in particular used to have a static package, but now it can't be installed without pulling in a bunch of Haskell development packages. The maintainer in this case refused to fix the problem and closes all bug reports without comment.
haskell is about the only thing on arch i'm not in love with. i also manually downloaded stack and am using it for xmonad/extensions/xmobar as well hledger now; it's been clean. highly recommended although it does use a lot of disk space - check out ~/.stack disk usage when time comes to pare down
Maybe one of the other packaging methods will give you a more stable installation ? https://hledger.org/download