Hackage changes render cabal.config settings inconsistent and result in configure failure

Story:
1. I used cabal freeze to have cabal.config in place.
2. Things were running smoothly for a couple of months.
3. Recently did 'cabal update'.
4. cabal install --only-dep stopped working with 'Dependency tree exhaustively searched'.
5. Applying a change to cabal.config solves problem:
- transformers-compat ==0.3.3.4,
- transformers-compat ==0.3.3.3,
6. Works again.

Now the real question:

How do I know why this suddenly stopped resolving? Did somebody change version ranges on some of dependent packages? How do i know which one got changed?