RE: TF GS P47 Build - yeah another bloody one!!
as a guess I would say you did not reduce power on the down leg of the loop?
All that is needed is a 1/2 wide strip of carbon fibre tape epoxied to the bottom of the spar from just inboard of the tip to same spot on opposite tip.
Mine will be around design weight or slightly higher but not enough to worry about and I will be putting on all the scale touches. This plane flies and lands beautifully even at 30 lbs, maybe you need to look at your techniques and building skills