I was mirroring my new plane and it copied it twice where I was deleting excess parts and I deleted the wrong part so I hit the redo button then half the parts turned into 4 f themselves in the same spot the I deleted the excess and hit re do and I had purple parts everywhere and I lost near three hours of progress on my plane
@Gestour I mirror stuff all the time and nothing bad happens
There's a solution to this. Don't mirror your plane ever, only mirror individual parts. And then save your work often, every couple of minutes, maybe even every time you add a part, avoid the undo button at all costs, just reload your plane at your most recent save point.
These issues are well known, and easily worked around.