Transient noise can couple through capacitive or magnetic isolation, creating a common-mode current between the primary and secondary sides. This emits EMI and can be exacerbated by a large return path. A Y-capacitor can connect the primary and secondary grounds together to minimize common-mode current return path size. The Y-capacitor effectively acts as a high-pass filter, creating a low impedance path for secondary-side high frequency signals to return back to the primary-side. The TPSI2072-Q1 EVM features an interlayer stitching capacitor by using the internal layers of the PCB to form a Y-capacitor (20 pF) across the primary and secondary side grounds. Connect the J11 jumper to enable the interlayer stitching capacitor. More about interlayer stitching capacitors can be read in the application report, Low-Emission Designs With ISOW7841 Integrated Signal and Power Isolator.