Are you working with a version control like git?
You surely committed/pushed or stashed more than once in your lifetime without previously saving everything in Visual Studio. Are you using "Panic Save"* since then?
At least this happened to me and my team a couple of times.
This extension saves all changes when you leave your current Visual Studio instance, e.g. when you switch to GitExtensions window for committing, stashing and pushing.
* Panic Save is the behavior when the user presses Ctrl+Shift+S repeatedly in a short amount of time, before switching to the GitExtensions (or any other) window
Please go to the github repository to file issues and start discussions.