As the DSP surge protection component is MOV type between L-N ,N-E, there may be a very small leakage current from Live to earth caused by the MOV normal operation. The RCD may see this as an imbalance between its live and neutral currents thereby causing the RCD to trip. Suggest fit the DSP before the RCD i.e. on the RCD’s input terminal side.
DSP is a device that is fitted in parallel across the L-N and earth.