Hello, it is not clear to me yet why a back to StockROM should be necessary. You’ve installed /e/ 0.7-2020022943260 and everything works fine?
If so, you can upgrade manually from e-Nougat to e-Pie immediately. Please compare with [HOWTO] Upgrade manually from e-Nougat | e-Oero to official e-Pie builds. This method has worked perfectly for me.