U4323QE, input lag using PBP from 4 inputs from the same machine

The Dell U4323QE experiences noticeable input lag when using Picture-by-Picture (PBP) mode with four inputs from the same machine (such as a quadrant display array). When connecting four outputs from the same PC (using an Nvidia P1000 graphics card), the input lag is significantly more pronounced compared to using a single 4K input.