I’ve witnessed it happen on a 6mm PPC benchrest rifle where the owner had switched barrels & either forgotten to apply the final torque or hadn’t applied enough.
Barrels on Mauser actions are typically installed with much greater torque than BR barrels - gunsmiths are far more likely to complain at the difficulty of removing rather than them being too loose. For one to ‘undo’ in use is bizarre & you’d have to imagine it wasn’t properly installed rather than had come loose (through vibration etc).