The problem
Retention dropped from roughly 25% to 5%, and the team didn't know why.
What I found
The product had turned off its ads. The ads were also an entry point back into the product, and nothing replaced it. Users who would have returned no longer had a path back in.
What we did
We added a new entry point in place of the one the ads had provided.
The result
That entry point alone recovered nearly all of the lost retention, a 20-point improvement over the post-drop baseline.