On the morning of January 2nd, I opened my laptop to find a colleague sharing an alert: our app was crashing for a substantial number of users. These crashes started happening out of nowhere on January 1st, specifically in the Stats feature of the app when accessing data for a specific date.
My immediate thought was that this had to be related to the date change to January 1st. ‘It’s not a coincidence,’ I confidently wrote on Slack. This led me down a debugging path that, frustratingly, didn’t reveal the root cause. I managed to develop a fix for the state that resulted in the crash, but I was baffled as to what was causing this state in the first place. ‘It must be because of January 1st,’ I thought again.
However, it took my colleague to point out some inconsistencies with the data format we were receiving from the backend. Was there a date-related issue on the backend, then? I tested the app locally with the December 31st version of the API, and the issue wasn’t present. I checked the repository history and noticed a change made on January 1st. This change was unrelated to the new year in any way. The issue, it turned out, could have happened on any day of the year.
It was just a coincidence.