Its been awhile since this happened to me. (it happened 3-4 times total on me)
I wrote out all the repro steps previously and hit submit and I guess i went over the char limit and it didnt submit, but I thought it had and refreshed page and lost it all. Too much to retype.
I remember it happening specifically after editing Animations and/or animationBP for the character and THEN in the MycharBP pressing CTRL Z three times in a row.
So create a basic animationBP and charBP. make the character do some animations like jump, crouch, etc… maybe a more complex one.
save it all and test… then with the mycharBP open, edit the animBP… maybe change out an animation for another. Then go into the animation and delete some frames of it so you’ve edit the animBP and an animation it uses directly. Then go to mycharBP and make a minor change. Then try ctrl z a few times in a row and see if you lose your settings on the BP. I think I compiled and saved when it happened each time as its a reflex these days… not sure if that matters tho.
i was doing something of that sort, every time it happened. I think it was on version 4.7.3. But im not sure.