Tried to build a certain 72k blocks per hour basalt generator and i've crafter the required 15 Hopper Minecart for the build in the Overworld, before of going into the Nether to build the contraption. After the finalisation of the build and a short testing , i've found out that none of the Minecart were picking items. After destroying them, recrafting them on the spot and putting them in the same place and environment ( Nether Roof, above a basalt delta, near a haste II beacon ) they were working perfectly .