Was using an open source piece of software for data storage and visualisation to work with the loggers my company makes. When importing old data for historical views, some of the csv imports would fail without any specific error messages.

It took me a couple of hours but after looking at their csv parser and making my own little one to test with, I eventually found out that it was all down to the way datatime (I think it was?) in java deals with DST, which apparently was to just fuck shit up.

Anyhow, a few simple lines added into the parser later and it all works just fine.

Was super proud of that one as it was the first time I actually looked somewhat good in front of my senior dev.