Someone once used to auto-format most of our code in his branch. He merged it 4 days long and deleted multiple changes in the trunk doing that. 3 months later I noticed that a few of my changes were just gone.

now just delete all the code he wrote but also add a whitespace on the end of every line

I had something like this happen to me with a bad rebase. Huge feature branch representing months of work by about a half-dozen people, and our coworker decides to rebase it instead of merging it into master. A bunch of random things just went poof. Would have been good if the deleted changes were completely deleted but we weren't that lucky. Instead a class file here would go missing while the instantiation of the class stayed behind. Sad lol.