Upgrade to the stock plywood belt holder. The problem with the plywood stack is that it is too short and the belt does not run parallel to itself/the axis. This meant that when tensioning the belt sufficiently with the idler pulley and wingnut, a lot down force on the smooth rods was created causing friction and or bending.
Simple 3D printed replacement with the existing hole separation for the M3 cap screws that arrach to the ply base of the bed or y carriage. Belt loops through both sides and zip ties together as before.
Hope you enjoy!