An example affected event was https://tools.wmflabs.org/grantmetrics/programs/Women_in_Red/Women_in_Red_-_February_hackathon
The per-wiki stats didn't add up to the totals at the top of the table. In reality, all the numbers are correct, they were just shown in the wrong order. Stupid developer 🤦 but good news is that the thoroughly tested backend was 100% accurate, phew!
Easy fix that I've already merged and deployed.
The retention numbers are still wrong though. For that I've filed T192742