In global configuration when using Mongo DB as storage type, the checkbox "Enable statistics logging of successful builds" only gets saved, when the status of "Enable Statistics logging" gets also changed.

E.g.:
Enable Statistics logging: true
Enable statistics logging of successful build: false

When you check "Enable statistics logging of successful build" and apply it, it won't get saved. It's still disabled.

But when you uncheck "Enable Statistics logging" AND check "Enable statistics logging of successful build", then both get saved correctly.

I created a pull reguest with a hotfix for this: https://github.com/jenkinsci/build-failure-analyzer-plugin/pull/38