Where did it all go wrong in my software project?

Perhaps churn_vs_complexity 1.4.0 can be of help with the new --timetravel mode.

https://rubygems.org/gems/churn_vs_complexity/versions/1.4.0

I just published version 1.2.0 of churn_vs_complexity (https://rubygems.org/gems/churn_vs_complexity).

It now supports short-hand flags for relative periods like "a month ago" (-m) and a nice summary function to give you aggregate datapoints to measure your codebase's health over time, which you could easily integrate into your CI.

It still includes the nice churn vs complexity graph output, now with revised logic for which observations are included and an improved calculation of churn.